1417 lines
		
	
	
		
			59 KiB
		
	
	
	
		
			Markdown
		
	
	
	
	
	
			
		
		
	
	
			1417 lines
		
	
	
		
			59 KiB
		
	
	
	
		
			Markdown
		
	
	
	
	
	
| <h1><img src="https://terser.org/img/terser-banner-logo.png" alt="Terser" width="400"></h1>
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| 
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|   [![NPM Version][npm-image]][npm-url]
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|   [![NPM Downloads][downloads-image]][downloads-url]
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|   [![CI pipeline][ci-image]][ci-url]
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|   [![Opencollective financial contributors][opencollective-contributors]][opencollective-url]
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| 
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| A JavaScript mangler/compressor toolkit for ES6+.
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| 
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| *note*: <s>You can support this project on patreon: [link]</s> **The Terser Patreon is shutting down in favor of opencollective**. Check out [PATRONS.md](https://github.com/terser/terser/blob/master/PATRONS.md) for our first-tier patrons.
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| 
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| Terser recommends you use RollupJS to bundle your modules, as that produces smaller code overall.
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| 
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| *Beautification* has been undocumented and is *being removed* from terser, we recommend you use [prettier](https://npmjs.com/package/prettier).
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| 
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| Find the changelog in [CHANGELOG.md](https://github.com/terser/terser/blob/master/CHANGELOG.md)
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| 
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| 
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| 
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| [npm-image]: https://img.shields.io/npm/v/terser.svg
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| [npm-url]: https://npmjs.org/package/terser
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| [downloads-image]: https://img.shields.io/npm/dm/terser.svg
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| [downloads-url]: https://npmjs.org/package/terser
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| [ci-image]: https://github.com/terser/terser/actions/workflows/ci.yml/badge.svg
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| [ci-url]: https://github.com/terser/terser/actions/workflows/ci.yml
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| [opencollective-contributors]: https://opencollective.com/terser/tiers/badge.svg
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| [opencollective-url]: https://opencollective.com/terser
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| 
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| Why choose terser?
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| ------------------
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| 
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| `uglify-es` is [no longer maintained](https://github.com/mishoo/UglifyJS2/issues/3156#issuecomment-392943058) and `uglify-js` does not support ES6+.
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| 
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| **`terser`** is a fork of `uglify-es` that mostly retains API and CLI compatibility
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| with `uglify-es` and `uglify-js@3`.
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| 
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| Install
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| -------
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| 
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| First make sure you have installed the latest version of [node.js](http://nodejs.org/)
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| (You may need to restart your computer after this step).
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| 
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| From NPM for use as a command line app:
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| 
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|     npm install terser -g
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| 
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| From NPM for programmatic use:
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| 
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|     npm install terser
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| 
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| # Command line usage
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| 
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| <!-- CLI_USAGE:START -->
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| 
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| ```
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| terser [input files] [options]
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| ```
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| 
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| Terser can take multiple input files.  It's recommended that you pass the
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| input files first, then pass the options.  Terser will parse input files
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| in sequence and apply any compression options.  The files are parsed in the
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| same global scope, that is, a reference from a file to some
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| variable/function declared in another file will be matched properly.
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| 
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| Command line arguments that take options (like --parse, --compress, --mangle and
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| --format) can take in a comma-separated list of default option overrides. For
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| instance:
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| 
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|     terser input.js --compress ecma=2015,computed_props=false
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| 
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| If no input file is specified, Terser will read from STDIN.
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| 
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| If you wish to pass your options before the input files, separate the two with
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| a double dash to prevent input files being used as option arguments:
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| 
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|     terser --compress --mangle -- input.js
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| 
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| ### Command line options
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| 
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| ```
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|     -h, --help                  Print usage information.
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|                                 `--help options` for details on available options.
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|     -V, --version               Print version number.
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|     -p, --parse <options>       Specify parser options:
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|                                 `acorn`  Use Acorn for parsing.
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|                                 `bare_returns`  Allow return outside of functions.
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|                                                 Useful when minifying CommonJS
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|                                                 modules and Userscripts that may
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|                                                 be anonymous function wrapped (IIFE)
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|                                                 by the .user.js engine `caller`.
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|                                 `expression`  Parse a single expression, rather than
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|                                               a program (for parsing JSON).
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|                                 `spidermonkey`  Assume input files are SpiderMonkey
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|                                                 AST format (as JSON).
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|     -c, --compress [options]    Enable compressor/specify compressor options:
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|                                 `pure_funcs`  List of functions that can be safely
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|                                               removed when their return values are
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|                                               not used.
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|     -m, --mangle [options]      Mangle names/specify mangler options:
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|                                 `reserved`  List of names that should not be mangled.
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|     --mangle-props [options]    Mangle properties/specify mangler options:
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|                                 `builtins`  Mangle property names that overlaps
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|                                             with standard JavaScript globals and DOM
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|                                             API props.
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|                                 `debug`  Add debug prefix and suffix.
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|                                 `keep_quoted`  Only mangle unquoted properties, quoted
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|                                                properties are automatically reserved.
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|                                                `strict` disables quoted properties
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|                                                being automatically reserved.
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|                                 `regex`  Only mangle matched property names.
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|                                 `only_annotated` Only mangle properties defined with /*@__MANGLE_PROP__*/.
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|                                 `reserved`  List of names that should not be mangled.
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|     -f, --format [options]      Specify format options.
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|                                 `preamble`  Preamble to prepend to the output. You
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|                                             can use this to insert a comment, for
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|                                             example for licensing information.
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|                                             This will not be parsed, but the source
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|                                             map will adjust for its presence.
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|                                 `quote_style`  Quote style:
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|                                                0 - auto
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|                                                1 - single
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|                                                2 - double
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|                                                3 - original
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|                                 `wrap_iife`  Wrap IIFEs in parenthesis. Note: you may
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|                                              want to disable `negate_iife` under
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|                                              compressor options.
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|                                 `wrap_func_args`  Wrap function arguments in parenthesis.
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|     -o, --output <file>         Output file path (default STDOUT). Specify `ast` or
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|                                 `spidermonkey` to write Terser or SpiderMonkey AST
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|                                 as JSON to STDOUT respectively.
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|     --comments [filter]         Preserve copyright comments in the output. By
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|                                 default this works like Google Closure, keeping
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|                                 JSDoc-style comments that contain e.g. "@license",
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|                                 or start with "!". You can optionally pass one of the
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|                                 following arguments to this flag:
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|                                 - "all" to keep all comments
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|                                 - `false` to omit comments in the output
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|                                 - a valid JS RegExp like `/foo/` or `/^!/` to
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|                                 keep only matching comments.
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|                                 Note that currently not *all* comments can be
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|                                 kept when compression is on, because of dead
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|                                 code removal or cascading statements into
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|                                 sequences.
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|     --config-file <file>        Read `minify()` options from JSON file.
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|     -d, --define <expr>[=value] Global definitions.
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|     --ecma <version>            Specify ECMAScript release: 5, 2015, 2016, etc.
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|     -e, --enclose [arg[:value]] Embed output in a big function with configurable
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|                                 arguments and values.
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|     --ie8                       Support non-standard Internet Explorer 8.
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|                                 Equivalent to setting `ie8: true` in `minify()`
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|                                 for `compress`, `mangle` and `format` options.
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|                                 By default Terser will not try to be IE-proof.
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|     --keep-classnames           Do not mangle/drop class names.
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|     --keep-fnames               Do not mangle/drop function names.  Useful for
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|                                 code relying on Function.prototype.name.
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|     --module                    Input is an ES6 module. If `compress` or `mangle` is
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|                                 enabled then the `toplevel` option will be enabled.
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|     --name-cache <file>         File to hold mangled name mappings.
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|     --safari10                  Support non-standard Safari 10/11.
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|                                 Equivalent to setting `safari10: true` in `minify()`
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|                                 for `mangle` and `format` options.
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|                                 By default `terser` will not work around
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|                                 Safari 10/11 bugs.
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|     --source-map [options]      Enable source map/specify source map options:
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|                                 `base`  Path to compute relative paths from input files.
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|                                 `content`  Input source map, useful if you're compressing
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|                                            JS that was generated from some other original
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|                                            code. Specify "inline" if the source map is
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|                                            included within the sources.
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|                                 `filename`  Name and/or location of the output source.
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|                                 `includeSources`  Pass this flag if you want to include
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|                                                   the content of source files in the
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|                                                   source map as sourcesContent property.
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|                                 `root`  Path to the original source to be included in
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|                                         the source map.
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|                                 `url`  If specified, path to the source map to append in
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|                                        `//# sourceMappingURL`.
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|     --timings                   Display operations run time on STDERR.
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|     --toplevel                  Compress and/or mangle variables in top level scope.
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|     --wrap <name>               Embed everything in a big function, making the
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|                                 “exports” and “global” variables available. You
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|                                 need to pass an argument to this option to
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|                                 specify the name that your module will take
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|                                 when included in, say, a browser.
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| ```
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| 
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| Specify `--output` (`-o`) to declare the output file.  Otherwise the output
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| goes to STDOUT.
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| 
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| ## CLI source map options
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| 
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| Terser can generate a source map file, which is highly useful for
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| debugging your compressed JavaScript.  To get a source map, pass
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| `--source-map --output output.js` (source map will be written out to
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| `output.js.map`).
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| 
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| Additional options:
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| 
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| - `--source-map "filename='<NAME>'"` to specify the name of the source map.
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| 
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| - `--source-map "root='<URL>'"` to pass the URL where the original files can be found.
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| 
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| - `--source-map "url='<URL>'"` to specify the URL where the source map can be found.
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|   Otherwise Terser assumes HTTP `X-SourceMap` is being used and will omit the
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|   `//# sourceMappingURL=` directive.
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| 
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| For example:
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| 
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|     terser js/file1.js js/file2.js \
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|              -o foo.min.js -c -m \
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|              --source-map "root='http://foo.com/src',url='foo.min.js.map'"
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| 
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| The above will compress and mangle `file1.js` and `file2.js`, will drop the
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| output in `foo.min.js` and the source map in `foo.min.js.map`.  The source
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| mapping will refer to `http://foo.com/src/js/file1.js` and
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| `http://foo.com/src/js/file2.js` (in fact it will list `http://foo.com/src`
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| as the source map root, and the original files as `js/file1.js` and
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| `js/file2.js`).
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| 
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| ### Composed source map
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| 
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| When you're compressing JS code that was output by a compiler such as
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| CoffeeScript, mapping to the JS code won't be too helpful.  Instead, you'd
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| like to map back to the original code (i.e. CoffeeScript).  Terser has an
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| option to take an input source map.  Assuming you have a mapping from
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| CoffeeScript → compiled JS, Terser can generate a map from CoffeeScript →
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| compressed JS by mapping every token in the compiled JS to its original
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| location.
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| 
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| To use this feature pass `--source-map "content='/path/to/input/source.map'"`
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| or `--source-map "content=inline"` if the source map is included inline with
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| the sources.
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| 
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| ## CLI compress options
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| 
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| You need to pass `--compress` (`-c`) to enable the compressor.  Optionally
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| you can pass a comma-separated list of [compress options](#compress-options).
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| 
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| Options are in the form `foo=bar`, or just `foo` (the latter implies
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| a boolean option that you want to set `true`; it's effectively a
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| shortcut for `foo=true`).
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| 
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| Example:
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| 
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|     terser file.js -c toplevel,sequences=false
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| 
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| ## CLI mangle options
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| 
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| To enable the mangler you need to pass `--mangle` (`-m`).  The following
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| (comma-separated) options are supported:
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| 
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| - `toplevel` (default `false`) -- mangle names declared in the top level scope.
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| 
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| - `eval` (default `false`) -- mangle names visible in scopes where `eval` or `with` are used.
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| 
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| When mangling is enabled but you want to prevent certain names from being
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| mangled, you can declare those names with `--mangle reserved` — pass a
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| comma-separated list of names.  For example:
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| 
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|     terser ... -m reserved=['$','require','exports']
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| 
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| to prevent the `require`, `exports` and `$` names from being changed.
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| 
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| ### CLI mangling property names (`--mangle-props`)
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| 
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| **Note:** THIS **WILL** BREAK YOUR CODE. A good rule of thumb is not to use this unless you know exactly what you're doing and how this works and read this section until the end.
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| 
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| Mangling property names is a separate step, different from variable name mangling.  Pass
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| `--mangle-props` to enable it. The least dangerous
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| way to use this is to use the `regex` option like so:
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| 
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| ```
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| terser example.js -c -m --mangle-props regex=/_$/
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| ```
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| 
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| This will mangle all properties that end with an
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| underscore. So you can use it to mangle internal methods.
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| 
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| By default, it will mangle all properties in the
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| input code with the exception of built in DOM properties and properties
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| in core JavaScript classes, which is what will break your code if you don't:
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| 
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| 1. Control all the code you're mangling
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| 2. Avoid using a module bundler, as they usually will call Terser on each file individually, making it impossible to pass mangled objects between modules.
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| 3. Avoid calling functions like `defineProperty` or `hasOwnProperty`, because they refer to object properties using strings and will break your code if you don't know what you are doing.
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| 
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| An example:
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| 
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| ```javascript
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| // example.js
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| var x = {
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|     baz_: 0,
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|     foo_: 1,
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|     calc: function() {
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|         return this.foo_ + this.baz_;
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|     }
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| };
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| x.bar_ = 2;
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| x["baz_"] = 3;
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| console.log(x.calc());
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| ```
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| Mangle all properties (except for JavaScript `builtins`) (**very** unsafe):
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| ```bash
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| $ terser example.js -c passes=2 -m --mangle-props
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| ```
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| ```javascript
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| var x={o:3,t:1,i:function(){return this.t+this.o},s:2};console.log(x.i());
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| ```
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| Mangle all properties except for `reserved` properties (still very unsafe):
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| ```bash
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| $ terser example.js -c passes=2 -m --mangle-props reserved=[foo_,bar_]
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| ```
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| ```javascript
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| var x={o:3,foo_:1,t:function(){return this.foo_+this.o},bar_:2};console.log(x.t());
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| ```
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| Mangle all properties matching a `regex` (not as unsafe but still unsafe):
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| ```bash
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| $ terser example.js -c passes=2 -m --mangle-props regex=/_$/
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| ```
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| ```javascript
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| var x={o:3,t:1,calc:function(){return this.t+this.o},i:2};console.log(x.calc());
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| ```
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| 
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| Combining mangle properties options:
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| ```bash
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| $ terser example.js -c passes=2 -m --mangle-props regex=/_$/,reserved=[bar_]
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| ```
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| ```javascript
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| var x={o:3,t:1,calc:function(){return this.t+this.o},bar_:2};console.log(x.calc());
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| ```
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| 
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| In order for this to be of any use, we avoid mangling standard JS names and DOM
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| API properties by default (`--mangle-props builtins` to override).
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| 
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| A regular expression can be used to define which property names should be
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| mangled.  For example, `--mangle-props regex=/^_/` will only mangle property
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| names that start with an underscore.
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| 
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| When you compress multiple files using this option, in order for them to
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| work together in the end we need to ensure somehow that one property gets
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| mangled to the same name in all of them.  For this, pass `--name-cache filename.json`
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| and Terser will maintain these mappings in a file which can then be reused.
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| It should be initially empty.  Example:
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| 
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| ```bash
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| $ rm -f /tmp/cache.json  # start fresh
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| $ terser file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js
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| $ terser file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js
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| ```
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| 
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| Now, `part1.js` and `part2.js` will be consistent with each other in terms
 | |
| of mangled property names.
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| 
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| Using the name cache is not necessary if you compress all your files in a
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| single call to Terser.
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| 
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| ### Mangling unquoted names (`--mangle-props keep_quoted`)
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| 
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| Using quoted property name (`o["foo"]`) reserves the property name (`foo`)
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| so that it is not mangled throughout the entire script even when used in an
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| unquoted style (`o.foo`). Example:
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| 
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| ```javascript
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| // stuff.js
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| var o = {
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|     "foo": 1,
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|     bar: 3
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| };
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| o.foo += o.bar;
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| console.log(o.foo);
 | |
| ```
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| ```bash
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| $ terser stuff.js --mangle-props keep_quoted -c -m
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| ```
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| ```javascript
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| var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo);
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| ```
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| 
 | |
| ### Debugging property name mangling
 | |
| 
 | |
| You can also pass `--mangle-props debug` in order to mangle property names
 | |
| without completely obscuring them. For example the property `o.foo`
 | |
| would mangle to `o._$foo$_` with this option. This allows property mangling
 | |
| of a large codebase while still being able to debug the code and identify
 | |
| where mangling is breaking things.
 | |
| 
 | |
| ```bash
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| $ terser stuff.js --mangle-props debug -c -m
 | |
| ```
 | |
| ```javascript
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| var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_);
 | |
| ```
 | |
| 
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| You can also pass a custom suffix using `--mangle-props debug=XYZ`. This would then
 | |
| mangle `o.foo` to `o._$foo$XYZ_`. You can change this each time you compile a
 | |
| script to identify how a property got mangled. One technique is to pass a
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| random number on every compile to simulate mangling changing with different
 | |
| inputs (e.g. as you update the input script with new properties), and to help
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| identify mistakes like writing mangled keys to storage.
 | |
| 
 | |
| <!-- CLI_USAGE:END -->
 | |
| 
 | |
| # API Reference
 | |
| 
 | |
| <!-- API_REFERENCE:START -->
 | |
| 
 | |
| Assuming installation via NPM, you can load Terser in your application
 | |
| like this:
 | |
| 
 | |
| ```javascript
 | |
| const { minify } = require("terser");
 | |
| ```
 | |
| 
 | |
| Or,
 | |
| 
 | |
| ```javascript
 | |
| import { minify } from "terser";
 | |
| ```
 | |
| 
 | |
| Browser loading is also supported:
 | |
| ```html
 | |
| <script src="https://cdn.jsdelivr.net/npm/source-map@0.7.3/dist/source-map.js"></script>
 | |
| <script src="https://cdn.jsdelivr.net/npm/terser/dist/bundle.min.js"></script>
 | |
| ```
 | |
| 
 | |
| There is a single async high level function, **`async minify(code, options)`**,
 | |
| which will perform all minification [phases](#minify-options) in a configurable
 | |
| manner. By default `minify()` will enable [`compress`](#compress-options)
 | |
| and [`mangle`](#mangle-options). Example:
 | |
| ```javascript
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| var code = "function add(first, second) { return first + second; }";
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| var result = await minify(code, { sourceMap: true });
 | |
| console.log(result.code);  // minified output: function add(n,d){return n+d}
 | |
| console.log(result.map);  // source map
 | |
| ```
 | |
| 
 | |
| You can `minify` more than one JavaScript file at a time by using an object
 | |
| for the first argument where the keys are file names and the values are source
 | |
| code:
 | |
| ```javascript
 | |
| var code = {
 | |
|     "file1.js": "function add(first, second) { return first + second; }",
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|     "file2.js": "console.log(add(1 + 2, 3 + 4));"
 | |
| };
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| var result = await minify(code);
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| console.log(result.code);
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| // function add(d,n){return d+n}console.log(add(3,7));
 | |
| ```
 | |
| 
 | |
| The `toplevel` option:
 | |
| ```javascript
 | |
| var code = {
 | |
|     "file1.js": "function add(first, second) { return first + second; }",
 | |
|     "file2.js": "console.log(add(1 + 2, 3 + 4));"
 | |
| };
 | |
| var options = { toplevel: true };
 | |
| var result = await minify(code, options);
 | |
| console.log(result.code);
 | |
| // console.log(3+7);
 | |
| ```
 | |
| 
 | |
| The `nameCache` option:
 | |
| ```javascript
 | |
| var options = {
 | |
|     mangle: {
 | |
|         toplevel: true,
 | |
|     },
 | |
|     nameCache: {}
 | |
| };
 | |
| var result1 = await minify({
 | |
|     "file1.js": "function add(first, second) { return first + second; }"
 | |
| }, options);
 | |
| var result2 = await minify({
 | |
|     "file2.js": "console.log(add(1 + 2, 3 + 4));"
 | |
| }, options);
 | |
| console.log(result1.code);
 | |
| // function n(n,r){return n+r}
 | |
| console.log(result2.code);
 | |
| // console.log(n(3,7));
 | |
| ```
 | |
| 
 | |
| You may persist the name cache to the file system in the following way:
 | |
| ```javascript
 | |
| var cacheFileName = "/tmp/cache.json";
 | |
| var options = {
 | |
|     mangle: {
 | |
|         properties: true,
 | |
|     },
 | |
|     nameCache: JSON.parse(fs.readFileSync(cacheFileName, "utf8"))
 | |
| };
 | |
| fs.writeFileSync("part1.js", await minify({
 | |
|     "file1.js": fs.readFileSync("file1.js", "utf8"),
 | |
|     "file2.js": fs.readFileSync("file2.js", "utf8")
 | |
| }, options).code, "utf8");
 | |
| fs.writeFileSync("part2.js", await minify({
 | |
|     "file3.js": fs.readFileSync("file3.js", "utf8"),
 | |
|     "file4.js": fs.readFileSync("file4.js", "utf8")
 | |
| }, options).code, "utf8");
 | |
| fs.writeFileSync(cacheFileName, JSON.stringify(options.nameCache), "utf8");
 | |
| ```
 | |
| 
 | |
| An example of a combination of `minify()` options:
 | |
| ```javascript
 | |
| var code = {
 | |
|     "file1.js": "function add(first, second) { return first + second; }",
 | |
|     "file2.js": "console.log(add(1 + 2, 3 + 4));"
 | |
| };
 | |
| var options = {
 | |
|     toplevel: true,
 | |
|     compress: {
 | |
|         global_defs: {
 | |
|             "@console.log": "alert"
 | |
|         },
 | |
|         passes: 2
 | |
|     },
 | |
|     format: {
 | |
|         preamble: "/* minified */"
 | |
|     }
 | |
| };
 | |
| var result = await minify(code, options);
 | |
| console.log(result.code);
 | |
| // /* minified */
 | |
| // alert(10);"
 | |
| ```
 | |
| 
 | |
| An error example:
 | |
| ```javascript
 | |
| try {
 | |
|     const result = await minify({"foo.js" : "if (0) else console.log(1);"});
 | |
|     // Do something with result
 | |
| } catch (error) {
 | |
|     const { message, filename, line, col, pos } = error;
 | |
|     // Do something with error
 | |
| }
 | |
| ```
 | |
| 
 | |
| ## Minify options
 | |
| 
 | |
| - `ecma` (default `undefined`) - pass `5`, `2015`, `2016`, etc to override
 | |
|   `compress` and `format`'s `ecma` options.
 | |
| 
 | |
| - `enclose` (default `false`) - pass `true`, or a string in the format
 | |
|   of `"args[:values]"`, where `args` and `values` are comma-separated
 | |
|   argument names and values, respectively, to embed the output in a big
 | |
|   function with the configurable arguments and values.
 | |
| 
 | |
| - `parse` (default `{}`) — pass an object if you wish to specify some
 | |
|   additional [parse options](#parse-options).
 | |
| 
 | |
| - `compress` (default `{}`) — pass `false` to skip compressing entirely.
 | |
|   Pass an object to specify custom [compress options](#compress-options).
 | |
| 
 | |
| - `mangle` (default `true`) — pass `false` to skip mangling names, or pass
 | |
|   an object to specify [mangle options](#mangle-options) (see below).
 | |
| 
 | |
|   - `mangle.properties` (default `false`) — a subcategory of the mangle option.
 | |
|     Pass an object to specify custom [mangle property options](#mangle-properties-options).
 | |
| 
 | |
| - `module` (default `false`) — Use when minifying an ES6 module. "use strict"
 | |
|   is implied and names can be mangled on the top scope. If `compress` or
 | |
|   `mangle` is enabled then the `toplevel` option will be enabled.
 | |
| 
 | |
| - `format` or `output` (default `null`) — pass an object if you wish to specify
 | |
|   additional [format options](#format-options).  The defaults are optimized
 | |
|   for best compression.
 | |
| 
 | |
| - `sourceMap` (default `false`) - pass an object if you wish to specify
 | |
|   [source map options](#source-map-options).
 | |
| 
 | |
| - `toplevel` (default `false`) - set to `true` if you wish to enable top level
 | |
|   variable and function name mangling and to drop unused variables and functions.
 | |
| 
 | |
| - `nameCache` (default `null`) - pass an empty object `{}` or a previously
 | |
|   used `nameCache` object if you wish to cache mangled variable and
 | |
|   property names across multiple invocations of `minify()`. Note: this is
 | |
|   a read/write property. `minify()` will read the name cache state of this
 | |
|   object and update it during minification so that it may be
 | |
|   reused or externally persisted by the user.
 | |
| 
 | |
| - `ie8` (default `false`) - set to `true` to support IE8.
 | |
| 
 | |
| - `keep_classnames` (default: `undefined`) - pass `true` to prevent discarding or mangling
 | |
|   of class names. Pass a regular expression to only keep class names matching that regex.
 | |
| 
 | |
| - `keep_fnames` (default: `false`) - pass `true` to prevent discarding or mangling
 | |
|   of function names. Pass a regular expression to only keep function names matching that regex.
 | |
|   Useful for code relying on `Function.prototype.name`. If the top level minify option
 | |
|   `keep_classnames` is `undefined` it will be overridden with the value of the top level
 | |
|   minify option `keep_fnames`.
 | |
| 
 | |
| - `safari10` (default: `false`) - pass `true` to work around Safari 10/11 bugs in
 | |
|   loop scoping and `await`. See `safari10` options in [`mangle`](#mangle-options)
 | |
|   and [`format`](#format-options) for details.
 | |
| 
 | |
| ## Minify options structure
 | |
| 
 | |
| ```javascript
 | |
| {
 | |
|     parse: {
 | |
|         // parse options
 | |
|     },
 | |
|     compress: {
 | |
|         // compress options
 | |
|     },
 | |
|     mangle: {
 | |
|         // mangle options
 | |
| 
 | |
|         properties: {
 | |
|             // mangle property options
 | |
|         }
 | |
|     },
 | |
|     format: {
 | |
|         // format options (can also use `output` for backwards compatibility)
 | |
|     },
 | |
|     sourceMap: {
 | |
|         // source map options
 | |
|     },
 | |
|     ecma: 5, // specify one of: 5, 2015, 2016, etc.
 | |
|     enclose: false, // or specify true, or "args:values"
 | |
|     keep_classnames: false,
 | |
|     keep_fnames: false,
 | |
|     ie8: false,
 | |
|     module: false,
 | |
|     nameCache: null, // or specify a name cache object
 | |
|     safari10: false,
 | |
|     toplevel: false
 | |
| }
 | |
| ```
 | |
| 
 | |
| ### Source map options
 | |
| 
 | |
| To generate a source map:
 | |
| ```javascript
 | |
| var result = await minify({"file1.js": "var a = function() {};"}, {
 | |
|     sourceMap: {
 | |
|         filename: "out.js",
 | |
|         url: "out.js.map"
 | |
|     }
 | |
| });
 | |
| console.log(result.code); // minified output
 | |
| console.log(result.map);  // source map
 | |
| ```
 | |
| 
 | |
| Note that the source map is not saved in a file, it's just returned in
 | |
| `result.map`.  The value passed for `sourceMap.url` is only used to set
 | |
| `//# sourceMappingURL=out.js.map` in `result.code`. The value of
 | |
| `filename` is only used to set `file` attribute (see [the spec][sm-spec])
 | |
| in source map file.
 | |
| 
 | |
| You can set option `sourceMap.url` to be `"inline"` and source map will
 | |
| be appended to code.
 | |
| 
 | |
| You can also specify sourceRoot property to be included in source map:
 | |
| ```javascript
 | |
| var result = await minify({"file1.js": "var a = function() {};"}, {
 | |
|     sourceMap: {
 | |
|         root: "http://example.com/src",
 | |
|         url: "out.js.map"
 | |
|     }
 | |
| });
 | |
| ```
 | |
| 
 | |
| If you're compressing compiled JavaScript and have a source map for it, you
 | |
| can use `sourceMap.content`:
 | |
| ```javascript
 | |
| var result = await minify({"compiled.js": "compiled code"}, {
 | |
|     sourceMap: {
 | |
|         content: "content from compiled.js.map",
 | |
|         url: "minified.js.map"
 | |
|     }
 | |
| });
 | |
| // same as before, it returns `code` and `map`
 | |
| ```
 | |
| 
 | |
| If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.url`.
 | |
| 
 | |
| If you happen to need the source map as a raw object, set `sourceMap.asObject` to `true`.
 | |
| 
 | |
| <!-- API_REFERENCE:END -->
 | |
| 
 | |
| <!-- OPTIONS:START -->
 | |
| 
 | |
| ## Parse options
 | |
| 
 | |
| - `bare_returns` (default `false`) -- support top level `return` statements
 | |
| 
 | |
| - `html5_comments` (default `true`)
 | |
| 
 | |
| - `shebang` (default `true`) -- support `#!command` as the first line
 | |
| 
 | |
| - `spidermonkey` (default `false`) -- accept a Spidermonkey (Mozilla) AST
 | |
| 
 | |
| ## Compress options
 | |
| 
 | |
| - `defaults` (default: `true`) -- Pass `false` to disable most default
 | |
|   enabled `compress` transforms. Useful when you only want to enable a few
 | |
|   `compress` options while disabling the rest.
 | |
| 
 | |
| - `arrows` (default: `true`) -- Class and object literal methods are converted
 | |
|   will also be converted to arrow expressions if the resultant code is shorter:
 | |
|   `m(){return x}` becomes `m:()=>x`. To do this to regular ES5 functions which
 | |
|   don't use `this` or `arguments`, see `unsafe_arrows`.
 | |
| 
 | |
| - `arguments` (default: `false`) -- replace `arguments[index]` with function
 | |
|   parameter name whenever possible.
 | |
| 
 | |
| - `booleans` (default: `true`) -- various optimizations for boolean context,
 | |
|   for example `!!a ? b : c → a ? b : c`
 | |
| 
 | |
| - `booleans_as_integers` (default: `false`) -- Turn booleans into 0 and 1, also
 | |
|   makes comparisons with booleans use `==` and `!=` instead of `===` and `!==`.
 | |
| 
 | |
| - `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables,
 | |
|   side effects permitting.
 | |
| 
 | |
| - `comparisons` (default: `true`) -- apply certain optimizations to binary nodes,
 | |
|   e.g. `!(a <= b) → a > b` (only when `unsafe_comps`), attempts to negate binary
 | |
|   nodes, e.g. `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc. Note: `comparisons`
 | |
|   works best with `lhs_constants` enabled.
 | |
| 
 | |
| - `computed_props` (default: `true`) -- Transforms constant computed properties
 | |
|   into regular ones: `{["computed"]: 1}` is converted to `{computed: 1}`.
 | |
| 
 | |
| - `conditionals` (default: `true`) -- apply optimizations for `if`-s and conditional
 | |
|   expressions
 | |
| 
 | |
| - `dead_code` (default: `true`) -- remove unreachable code
 | |
| 
 | |
| - `directives` (default: `true`) -- remove redundant or non-standard directives
 | |
| 
 | |
| - `drop_console` (default: `false`) -- Pass `true` to discard calls to
 | |
|   `console.*` functions. If you wish to drop a specific function call
 | |
|   such as `console.info` and/or retain side effects from function arguments
 | |
|   after dropping the function call then use `pure_funcs` instead.
 | |
| 
 | |
| - `drop_debugger` (default: `true`) -- remove `debugger;` statements
 | |
| 
 | |
| - `ecma` (default: `5`) -- Pass `2015` or greater to enable `compress` options that
 | |
|   will transform ES5 code into smaller ES6+ equivalent forms.
 | |
| 
 | |
| - `evaluate` (default: `true`) -- attempt to evaluate constant expressions
 | |
| 
 | |
| - `expression` (default: `false`) -- Pass `true` to preserve completion values
 | |
|   from terminal statements without `return`, e.g. in bookmarklets.
 | |
| 
 | |
| - `global_defs` (default: `{}`) -- see [conditional compilation](#conditional-compilation)
 | |
| 
 | |
| - `hoist_funs` (default: `false`) -- hoist function declarations
 | |
| 
 | |
| - `hoist_props` (default: `true`) -- hoist properties from constant object and
 | |
|   array literals into regular variables subject to a set of constraints. For example:
 | |
|   `var o={p:1, q:2}; f(o.p, o.q);` is converted to `f(1, 2);`. Note: `hoist_props`
 | |
|   works best with `mangle` enabled, the `compress` option `passes` set to `2` or higher,
 | |
|   and the `compress` option `toplevel` enabled.
 | |
| 
 | |
| - `hoist_vars` (default: `false`) -- hoist `var` declarations (this is `false`
 | |
|   by default because it seems to increase the size of the output in general)
 | |
| 
 | |
| - `if_return` (default: `true`) -- optimizations for if/return and if/continue
 | |
| 
 | |
| - `inline` (default: `true`) -- inline calls to function with simple/`return` statement:
 | |
|   - `false` -- same as `0`
 | |
|   - `0` -- disabled inlining
 | |
|   - `1` -- inline simple functions
 | |
|   - `2` -- inline functions with arguments
 | |
|   - `3` -- inline functions with arguments and variables
 | |
|   - `true` -- same as `3`
 | |
| 
 | |
| - `join_vars` (default: `true`) -- join consecutive `var`, `let` and `const` statements
 | |
| 
 | |
| - `keep_classnames` (default: `false`) -- Pass `true` to prevent the compressor from
 | |
|   discarding class names. Pass a regular expression to only keep class names matching
 | |
|   that regex. See also: the `keep_classnames` [mangle option](#mangle-options).
 | |
| 
 | |
| - `keep_fargs` (default: `true`) -- Prevents the compressor from discarding unused
 | |
|   function arguments.  You need this for code which relies on `Function.length`.
 | |
| 
 | |
| - `keep_fnames` (default: `false`) -- Pass `true` to prevent the
 | |
|   compressor from discarding function names. Pass a regular expression to only keep
 | |
|   function names matching that regex. Useful for code relying on `Function.prototype.name`.
 | |
|   See also: the `keep_fnames` [mangle option](#mangle-options).
 | |
| 
 | |
| - `keep_infinity` (default: `false`) -- Pass `true` to prevent `Infinity` from
 | |
|   being compressed into `1/0`, which may cause performance issues on Chrome.
 | |
| 
 | |
| - `lhs_constants` (default: `true`) -- Moves constant values to the left-hand side
 | |
|   of binary nodes. `foo == 42 → 42 == foo`
 | |
| 
 | |
| - `loops` (default: `true`) -- optimizations for `do`, `while` and `for` loops
 | |
|   when we can statically determine the condition.
 | |
| 
 | |
| - `module` (default `false`) -- Pass `true` when compressing an ES6 module. Strict
 | |
|   mode is implied and the `toplevel` option as well.
 | |
| 
 | |
| - `negate_iife` (default: `true`) -- negate "Immediately-Called Function Expressions"
 | |
|   where the return value is discarded, to avoid the parens that the
 | |
|   code generator would insert.
 | |
| 
 | |
| - `passes` (default: `1`) -- The maximum number of times to run compress.
 | |
|   In some cases more than one pass leads to further compressed code.  Keep in
 | |
|   mind more passes will take more time.
 | |
| 
 | |
| - `properties` (default: `true`) -- rewrite property access using the dot notation, for
 | |
|   example `foo["bar"] → foo.bar`
 | |
| 
 | |
| - `pure_funcs` (default: `null`) -- You can pass an array of names and
 | |
|   Terser will assume that those functions do not produce side
 | |
|   effects.  DANGER: will not check if the name is redefined in scope.
 | |
|   An example case here, for instance `var q = Math.floor(a/b)`.  If
 | |
|   variable `q` is not used elsewhere, Terser will drop it, but will
 | |
|   still keep the `Math.floor(a/b)`, not knowing what it does.  You can
 | |
|   pass `pure_funcs: [ 'Math.floor' ]` to let it know that this
 | |
|   function won't produce any side effect, in which case the whole
 | |
|   statement would get discarded.  The current implementation adds some
 | |
|   overhead (compression will be slower).
 | |
| 
 | |
| - `pure_getters` (default: `"strict"`) -- If you pass `true` for
 | |
|   this, Terser will assume that object property access
 | |
|   (e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects.
 | |
|   Specify `"strict"` to treat `foo.bar` as side-effect-free only when
 | |
|   `foo` is certain to not throw, i.e. not `null` or `undefined`.
 | |
| 
 | |
| - `reduce_vars` (default: `true`) -- Improve optimization on variables assigned with and
 | |
|   used as constant values.
 | |
| 
 | |
| - `reduce_funcs` (default: `true`) -- Inline single-use functions when
 | |
|   possible. Depends on `reduce_vars` being enabled.  Disabling this option
 | |
|   sometimes improves performance of the output code.
 | |
| 
 | |
| - `sequences` (default: `true`) -- join consecutive simple statements using the
 | |
|   comma operator.  May be set to a positive integer to specify the maximum number
 | |
|   of consecutive comma sequences that will be generated. If this option is set to
 | |
|   `true` then the default `sequences` limit is `200`. Set option to `false` or `0`
 | |
|   to disable. The smallest `sequences` length is `2`. A `sequences` value of `1`
 | |
|   is grandfathered to be equivalent to `true` and as such means `200`. On rare
 | |
|   occasions the default sequences limit leads to very slow compress times in which
 | |
|   case a value of `20` or less is recommended.
 | |
| 
 | |
| - `side_effects` (default: `true`) -- Remove expressions which have no side effects
 | |
|   and whose results aren't used.
 | |
| 
 | |
| - `switches` (default: `true`) -- de-duplicate and remove unreachable `switch` branches
 | |
| 
 | |
| - `toplevel` (default: `false`) -- drop unreferenced functions (`"funcs"`) and/or
 | |
|   variables (`"vars"`) in the top level scope (`false` by default, `true` to drop
 | |
|   both unreferenced functions and variables)
 | |
| 
 | |
| - `top_retain` (default: `null`) -- prevent specific toplevel functions and
 | |
|   variables from `unused` removal (can be array, comma-separated, RegExp or
 | |
|   function. Implies `toplevel`)
 | |
| 
 | |
| - `typeofs` (default: `true`) -- Transforms `typeof foo == "undefined"` into
 | |
|   `foo === void 0`.  Note: recommend to set this value to `false` for IE10 and
 | |
|   earlier versions due to known issues.
 | |
| 
 | |
| - `unsafe` (default: `false`) -- apply "unsafe" transformations
 | |
|   ([details](#the-unsafe-compress-option)).
 | |
| 
 | |
| - `unsafe_arrows` (default: `false`) -- Convert ES5 style anonymous function
 | |
|   expressions to arrow functions if the function body does not reference `this`.
 | |
|   Note: it is not always safe to perform this conversion if code relies on the
 | |
|   the function having a `prototype`, which arrow functions lack.
 | |
|   This transform requires that the `ecma` compress option is set to `2015` or greater.
 | |
| 
 | |
| - `unsafe_comps` (default: `false`) -- Reverse `<` and `<=` to `>` and `>=` to
 | |
|   allow improved compression. This might be unsafe when an at least one of two
 | |
|   operands is an object with computed values due the use of methods like `get`,
 | |
|   or `valueOf`. This could cause change in execution order after operands in the
 | |
|   comparison are switching. Compression only works if both `comparisons` and
 | |
|   `unsafe_comps` are both set to true.
 | |
| 
 | |
| - `unsafe_Function` (default: `false`) -- compress and mangle `Function(args, code)`
 | |
|   when both `args` and `code` are string literals.
 | |
| 
 | |
| - `unsafe_math` (default: `false`) -- optimize numerical expressions like
 | |
|   `2 * x * 3` into `6 * x`, which may give imprecise floating point results.
 | |
| 
 | |
| - `unsafe_symbols` (default: `false`) -- removes keys from native Symbol
 | |
|   declarations, e.g `Symbol("kDog")` becomes `Symbol()`.
 | |
| 
 | |
| - `unsafe_methods` (default: false) -- Converts `{ m: function(){} }` to
 | |
|   `{ m(){} }`. `ecma` must be set to `6` or greater to enable this transform.
 | |
|   If `unsafe_methods` is a RegExp then key/value pairs with keys matching the
 | |
|   RegExp will be converted to concise methods.
 | |
|   Note: if enabled there is a risk of getting a "`<method name>` is not a
 | |
|   constructor" TypeError should any code try to `new` the former function.
 | |
| 
 | |
| - `unsafe_proto` (default: `false`) -- optimize expressions like
 | |
|   `Array.prototype.slice.call(a)` into `[].slice.call(a)`
 | |
| 
 | |
| - `unsafe_regexp` (default: `false`) -- enable substitutions of variables with
 | |
|   `RegExp` values the same way as if they are constants.
 | |
| 
 | |
| - `unsafe_undefined` (default: `false`) -- substitute `void 0` if there is a
 | |
|   variable named `undefined` in scope (variable name will be mangled, typically
 | |
|   reduced to a single character)
 | |
| 
 | |
| - `unused` (default: `true`) -- drop unreferenced functions and variables (simple
 | |
|   direct variable assignments do not count as references unless set to `"keep_assign"`)
 | |
| 
 | |
| ## Mangle options
 | |
| 
 | |
| - `eval` (default `false`) -- Pass `true` to mangle names visible in scopes
 | |
|   where `eval` or `with` are used.
 | |
| 
 | |
| - `keep_classnames` (default `false`) -- Pass `true` to not mangle class names.
 | |
|   Pass a regular expression to only keep class names matching that regex.
 | |
|   See also: the `keep_classnames` [compress option](#compress-options).
 | |
| 
 | |
| - `keep_fnames` (default `false`) -- Pass `true` to not mangle function names.
 | |
|   Pass a regular expression to only keep function names matching that regex.
 | |
|   Useful for code relying on `Function.prototype.name`. See also: the `keep_fnames`
 | |
|   [compress option](#compress-options).
 | |
| 
 | |
| - `module` (default `false`) -- Pass `true` an ES6 modules, where the toplevel
 | |
|   scope is not the global scope. Implies `toplevel`.
 | |
| 
 | |
| - `nth_identifier` (default: an internal mangler that weights based on character
 | |
|   frequency analysis) -- Pass an object with a `get(n)` function that converts an
 | |
|   ordinal into the nth most favored (usually shortest) identifier.
 | |
|   Optionally also provide `reset()`, `sort()`, and `consider(chars, delta)` to
 | |
|   use character frequency analysis of the source code.
 | |
| 
 | |
| - `reserved` (default `[]`) -- Pass an array of identifiers that should be
 | |
|   excluded from mangling. Example: `["foo", "bar"]`.
 | |
| 
 | |
| - `toplevel` (default `false`) -- Pass `true` to mangle names declared in the
 | |
|   top level scope.
 | |
| 
 | |
| - `safari10` (default `false`) -- Pass `true` to work around the Safari 10 loop
 | |
|   iterator [bug](https://bugs.webkit.org/show_bug.cgi?id=171041)
 | |
|   "Cannot declare a let variable twice".
 | |
|   See also: the `safari10` [format option](#format-options).
 | |
| 
 | |
| Examples:
 | |
| 
 | |
| ```javascript
 | |
| // test.js
 | |
| var globalVar;
 | |
| function funcName(firstLongName, anotherLongName) {
 | |
|     var myVariable = firstLongName +  anotherLongName;
 | |
| }
 | |
| ```
 | |
| ```javascript
 | |
| var code = fs.readFileSync("test.js", "utf8");
 | |
| 
 | |
| await minify(code).code;
 | |
| // 'function funcName(a,n){}var globalVar;'
 | |
| 
 | |
| await minify(code, { mangle: { reserved: ['firstLongName'] } }).code;
 | |
| // 'function funcName(firstLongName,a){}var globalVar;'
 | |
| 
 | |
| await minify(code, { mangle: { toplevel: true } }).code;
 | |
| // 'function n(n,a){}var a;'
 | |
| ```
 | |
| 
 | |
| ### Mangle properties options
 | |
| 
 | |
| - `builtins` (default: `false`) — Use `true` to allow the mangling of builtin
 | |
|   DOM properties. Not recommended to override this setting.
 | |
| 
 | |
| - `debug` (default: `false`) — Mangle names with the original name still present.
 | |
|   Pass an empty string `""` to enable, or a non-empty string to set the debug suffix.
 | |
| 
 | |
| - `keep_quoted` (default: `false`) — How quoting properties (`{"prop": ...}` and `obj["prop"]`) controls what gets mangled.
 | |
|   - `"strict"` (recommended) -- `obj.prop` is mangled.
 | |
|   - `false` -- `obj["prop"]` is mangled.
 | |
|   - `true` -- `obj.prop` is mangled unless there is `obj["prop"]` elsewhere in the code.
 | |
| 
 | |
| - `nth_identifer` (default: an internal mangler that weights based on character
 | |
|   frequency analysis) -- Pass an object with a `get(n)` function that converts an
 | |
|   ordinal into the nth most favored (usually shortest) identifier.
 | |
|   Optionally also provide `reset()`, `sort()`, and `consider(chars, delta)` to
 | |
|   use character frequency analysis of the source code.
 | |
| 
 | |
| - `regex` (default: `null`) — Pass a [RegExp literal or pattern string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) to only mangle property matching the regular expression.
 | |
| 
 | |
| - `reserved` (default: `[]`) — Do not mangle property names listed in the
 | |
|   `reserved` array.
 | |
| 
 | |
| - `undeclared` (default: `false`) - Mangle those names when they are accessed
 | |
|   as properties of known top level variables but their declarations are never
 | |
|   found in input code. May be useful when only minifying parts of a project.
 | |
|   See [#397](https://github.com/terser/terser/issues/397) for more details.
 | |
| 
 | |
| 
 | |
| ## Format options
 | |
| 
 | |
| These options control the format of Terser's output code. Previously known
 | |
| as "output options".
 | |
| 
 | |
| - `ascii_only` (default `false`) -- escape Unicode characters in strings and
 | |
|   regexps (affects directives with non-ascii characters becoming invalid)
 | |
| 
 | |
| - `beautify` (default `false`) -- (DEPRECATED) whether to beautify the output.
 | |
|   When using the legacy `-b` CLI flag, this is set to true by default.
 | |
| 
 | |
| - `braces` (default `false`) -- always insert braces in `if`, `for`,
 | |
|   `do`, `while` or `with` statements, even if their body is a single
 | |
|   statement.
 | |
| 
 | |
| - `comments` (default `"some"`) -- by default it keeps JSDoc-style comments
 | |
|   that contain "@license", "@copyright", "@preserve" or start with `!`, pass `true`
 | |
|   or `"all"` to preserve all comments, `false` to omit comments in the output,
 | |
|   a regular expression string (e.g. `/^!/`) or a function.
 | |
| 
 | |
| - `ecma` (default `5`) -- set desired EcmaScript standard version for output.
 | |
|   Set `ecma` to `2015` or greater to emit shorthand object properties - i.e.:
 | |
|   `{a}` instead of `{a: a}`.  The `ecma` option will only change the output in
 | |
|   direct control of the beautifier. Non-compatible features in your input will
 | |
|   still be output as is. For example: an `ecma` setting of `5` will **not**
 | |
|   convert modern code to ES5.
 | |
| 
 | |
| - `indent_level` (default `4`)
 | |
| 
 | |
| - `indent_start` (default `0`) -- prefix all lines by that many spaces
 | |
| 
 | |
| - `inline_script` (default `true`) -- escape HTML comments and the slash in
 | |
|   occurrences of `</script>` in strings
 | |
| 
 | |
| - `keep_numbers` (default `false`) -- keep number literals as it was in original code
 | |
|  (disables optimizations like converting `1000000` into `1e6`)
 | |
| 
 | |
| - `keep_quoted_props` (default `false`) -- when turned on, prevents stripping
 | |
|   quotes from property names in object literals.
 | |
| 
 | |
| - `max_line_len` (default `false`) -- maximum line length (for minified code)
 | |
| 
 | |
| - `preamble` (default `null`) -- when passed it must be a string and
 | |
|   it will be prepended to the output literally.  The source map will
 | |
|   adjust for this text.  Can be used to insert a comment containing
 | |
|   licensing information, for example.
 | |
| 
 | |
| - `quote_keys` (default `false`) -- pass `true` to quote all keys in literal
 | |
|   objects
 | |
| 
 | |
| - `quote_style` (default `0`) -- preferred quote style for strings (affects
 | |
|   quoted property names and directives as well):
 | |
|   - `0` -- prefers double quotes, switches to single quotes when there are
 | |
|     more double quotes in the string itself. `0` is best for gzip size.
 | |
|   - `1` -- always use single quotes
 | |
|   - `2` -- always use double quotes
 | |
|   - `3` -- always use the original quotes
 | |
| 
 | |
| - `preserve_annotations` -- (default `false`) -- Preserve [Terser annotations](#annotations) in the output.
 | |
| 
 | |
| - `safari10` (default `false`) -- set this option to `true` to work around
 | |
|   the [Safari 10/11 await bug](https://bugs.webkit.org/show_bug.cgi?id=176685).
 | |
|   See also: the `safari10` [mangle option](#mangle-options).
 | |
| 
 | |
| - `semicolons` (default `true`) -- separate statements with semicolons.  If
 | |
|   you pass `false` then whenever possible we will use a newline instead of a
 | |
|   semicolon, leading to more readable output of minified code (size before
 | |
|   gzip could be smaller; size after gzip insignificantly larger).
 | |
| 
 | |
| - `shebang` (default `true`) -- preserve shebang `#!` in preamble (bash scripts)
 | |
| 
 | |
| - `spidermonkey` (default `false`) -- produce a Spidermonkey (Mozilla) AST
 | |
| 
 | |
| - `webkit` (default `false`) -- enable workarounds for WebKit bugs.
 | |
|   PhantomJS users should set this option to `true`.
 | |
| 
 | |
| - `wrap_iife` (default `false`) -- pass `true` to wrap immediately invoked
 | |
|   function expressions. See
 | |
|   [#640](https://github.com/mishoo/UglifyJS2/issues/640) for more details.
 | |
| 
 | |
| - `wrap_func_args` (default `true`) -- pass `false` if you do not want to wrap
 | |
|   function expressions that are passed as arguments, in parenthesis. See
 | |
|   [OptimizeJS](https://github.com/nolanlawson/optimize-js) for more details.
 | |
| 
 | |
| 
 | |
| <!-- OPTIONS:END -->
 | |
| 
 | |
| 
 | |
| # Miscellaneous
 | |
| 
 | |
| <!-- MISCELLANEOUS:START -->
 | |
| 
 | |
| ### Keeping copyright notices or other comments
 | |
| 
 | |
| You can pass `--comments` to retain certain comments in the output.  By
 | |
| default it will keep comments starting with "!" and JSDoc-style comments that
 | |
| contain "@preserve", "@copyright", "@license" or "@cc_on" (conditional compilation for IE).
 | |
| You can pass `--comments all` to keep all the comments, or a valid JavaScript regexp to
 | |
| keep only comments that match this regexp.  For example `--comments /^!/`
 | |
| will keep comments like `/*! Copyright Notice */`.
 | |
| 
 | |
| Note, however, that there might be situations where comments are lost.  For
 | |
| example:
 | |
| ```javascript
 | |
| function f() {
 | |
|     /** @preserve Foo Bar */
 | |
|     function g() {
 | |
|         // this function is never called
 | |
|     }
 | |
|     return something();
 | |
| }
 | |
| ```
 | |
| 
 | |
| Even though it has "@preserve", the comment will be lost because the inner
 | |
| function `g` (which is the AST node to which the comment is attached to) is
 | |
| discarded by the compressor as not referenced.
 | |
| 
 | |
| The safest comments where to place copyright information (or other info that
 | |
| needs to be kept in the output) are comments attached to toplevel nodes.
 | |
| 
 | |
| ### The `unsafe` `compress` option
 | |
| 
 | |
| It enables some transformations that *might* break code logic in certain
 | |
| contrived cases, but should be fine for most code.  It assumes that standard
 | |
| built-in ECMAScript functions and classes have not been altered or replaced.
 | |
| You might want to try it on your own code; it should reduce the minified size.
 | |
| Some examples of the optimizations made when this option is enabled:
 | |
| 
 | |
| - `new Array(1, 2, 3)` or `Array(1, 2, 3)` → `[ 1, 2, 3 ]`
 | |
| - `Array.from([1, 2, 3])` → `[1, 2, 3]`
 | |
| - `new Object()` → `{}`
 | |
| - `String(exp)` or `exp.toString()` → `"" + exp`
 | |
| - `new Object/RegExp/Function/Error/Array (...)` → we discard the `new`
 | |
| - `"foo bar".substr(4)` → `"bar"`
 | |
| 
 | |
| ### Conditional compilation
 | |
| 
 | |
| You can use the `--define` (`-d`) switch in order to declare global
 | |
| variables that Terser will assume to be constants (unless defined in
 | |
| scope).  For example if you pass `--define DEBUG=false` then, coupled with
 | |
| dead code removal Terser will discard the following from the output:
 | |
| ```javascript
 | |
| if (DEBUG) {
 | |
|     console.log("debug stuff");
 | |
| }
 | |
| ```
 | |
| 
 | |
| You can specify nested constants in the form of `--define env.DEBUG=false`.
 | |
| 
 | |
| Another way of doing that is to declare your globals as constants in a
 | |
| separate file and include it into the build.  For example you can have a
 | |
| `build/defines.js` file with the following:
 | |
| ```javascript
 | |
| var DEBUG = false;
 | |
| var PRODUCTION = true;
 | |
| // etc.
 | |
| ```
 | |
| 
 | |
| and build your code like this:
 | |
| 
 | |
|     terser build/defines.js js/foo.js js/bar.js... -c
 | |
| 
 | |
| Terser will notice the constants and, since they cannot be altered, it
 | |
| will evaluate references to them to the value itself and drop unreachable
 | |
| code as usual.  The build will contain the `const` declarations if you use
 | |
| them. If you are targeting < ES6 environments which does not support `const`,
 | |
| using `var` with `reduce_vars` (enabled by default) should suffice.
 | |
| 
 | |
| ### Conditional compilation API
 | |
| 
 | |
| You can also use conditional compilation via the programmatic API. With the difference that the
 | |
| property name is `global_defs` and is a compressor property:
 | |
| 
 | |
| ```javascript
 | |
| var result = await minify(fs.readFileSync("input.js", "utf8"), {
 | |
|     compress: {
 | |
|         dead_code: true,
 | |
|         global_defs: {
 | |
|             DEBUG: false
 | |
|         }
 | |
|     }
 | |
| });
 | |
| ```
 | |
| 
 | |
| To replace an identifier with an arbitrary non-constant expression it is
 | |
| necessary to prefix the `global_defs` key with `"@"` to instruct Terser
 | |
| to parse the value as an expression:
 | |
| ```javascript
 | |
| await minify("alert('hello');", {
 | |
|     compress: {
 | |
|         global_defs: {
 | |
|             "@alert": "console.log"
 | |
|         }
 | |
|     }
 | |
| }).code;
 | |
| // returns: 'console.log("hello");'
 | |
| ```
 | |
| 
 | |
| Otherwise it would be replaced as string literal:
 | |
| ```javascript
 | |
| await minify("alert('hello');", {
 | |
|     compress: {
 | |
|         global_defs: {
 | |
|             "alert": "console.log"
 | |
|         }
 | |
|     }
 | |
| }).code;
 | |
| // returns: '"console.log"("hello");'
 | |
| ```
 | |
| 
 | |
| ### Annotations
 | |
| 
 | |
| Annotations in Terser are a way to tell it to treat a certain function call differently. The following annotations are available:
 | |
| 
 | |
|  * `/*@__INLINE__*/` - forces a function to be inlined somewhere.
 | |
|  * `/*@__NOINLINE__*/` - Makes sure the called function is not inlined into the call site.
 | |
|  * `/*@__PURE__*/` - Marks a function call as pure. That means, it can safely be dropped.
 | |
|  * `/*@__KEY__*/` - Marks a string literal as a property to also mangle it when mangling properties.
 | |
|  * `/*@__MANGLE_PROP__*/` - Opts-in an object property (or class field) for mangling, when the property mangler is enabled.
 | |
| 
 | |
| You can use either a `@` sign at the start, or a `#`.
 | |
| 
 | |
| Here are some examples on how to use them:
 | |
| 
 | |
| ```javascript
 | |
| /*@__INLINE__*/
 | |
| function_always_inlined_here()
 | |
| 
 | |
| /*#__NOINLINE__*/
 | |
| function_cant_be_inlined_into_here()
 | |
| 
 | |
| const x = /*#__PURE__*/i_am_dropped_if_x_is_not_used()
 | |
| 
 | |
| function lookup(object, key) { return object[key]; }
 | |
| lookup({ i_will_be_mangled_too: "bar" }, /*@__KEY__*/ "i_will_be_mangled_too");
 | |
| ```
 | |
| 
 | |
| ### ESTree / SpiderMonkey AST
 | |
| 
 | |
| Terser has its own abstract syntax tree format; for
 | |
| [practical reasons](http://lisperator.net/blog/uglifyjs-why-not-switching-to-spidermonkey-ast/)
 | |
| we can't easily change to using the SpiderMonkey AST internally.  However,
 | |
| Terser now has a converter which can import a SpiderMonkey AST.
 | |
| 
 | |
| For example [Acorn][acorn] is a super-fast parser that produces a
 | |
| SpiderMonkey AST.  It has a small CLI utility that parses one file and dumps
 | |
| the AST in JSON on the standard output.  To use Terser to mangle and
 | |
| compress that:
 | |
| 
 | |
|     acorn file.js | terser -p spidermonkey -m -c
 | |
| 
 | |
| The `-p spidermonkey` option tells Terser that all input files are not
 | |
| JavaScript, but JS code described in SpiderMonkey AST in JSON.  Therefore we
 | |
| don't use our own parser in this case, but just transform that AST into our
 | |
| internal AST.
 | |
| 
 | |
| `spidermonkey` is also available in `minify` as `parse` and `format` options to
 | |
| accept and/or produce a spidermonkey AST.
 | |
| 
 | |
| ### Use Acorn for parsing
 | |
| 
 | |
| More for fun, I added the `-p acorn` option which will use Acorn to do all
 | |
| the parsing.  If you pass this option, Terser will `require("acorn")`.
 | |
| 
 | |
| Acorn is really fast (e.g. 250ms instead of 380ms on some 650K code), but
 | |
| converting the SpiderMonkey tree that Acorn produces takes another 150ms so
 | |
| in total it's a bit more than just using Terser's own parser.
 | |
| 
 | |
| [acorn]: https://github.com/ternjs/acorn
 | |
| [sm-spec]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k
 | |
| 
 | |
| ### Terser Fast Minify Mode
 | |
| 
 | |
| It's not well known, but whitespace removal and symbol mangling accounts
 | |
| for 95% of the size reduction in minified code for most JavaScript - not
 | |
| elaborate code transforms. One can simply disable `compress` to speed up
 | |
| Terser builds by 3 to 4 times.
 | |
| 
 | |
| | d3.js | size | gzip size | time (s) |
 | |
| |   --- | ---: |      ---: |     ---: |
 | |
| | original                                    | 451,131 | 108,733 |     - |
 | |
| | terser@3.7.5 mangle=false, compress=false   | 316,600 |  85,245 |  0.82 |
 | |
| | terser@3.7.5 mangle=true, compress=false    | 220,216 |  72,730 |  1.45 |
 | |
| | terser@3.7.5 mangle=true, compress=true     | 212,046 |  70,954 |  5.87 |
 | |
| | babili@0.1.4                                | 210,713 |  72,140 | 12.64 |
 | |
| | babel-minify@0.4.3                          | 210,321 |  72,242 | 48.67 |
 | |
| | babel-minify@0.5.0-alpha.01eac1c3           | 210,421 |  72,238 | 14.17 |
 | |
| 
 | |
| To enable fast minify mode from the CLI use:
 | |
| ```
 | |
| terser file.js -m
 | |
| ```
 | |
| To enable fast minify mode with the API use:
 | |
| ```js
 | |
| await minify(code, { compress: false, mangle: true });
 | |
| ```
 | |
| 
 | |
| #### Source maps and debugging
 | |
| 
 | |
| Various `compress` transforms that simplify, rearrange, inline and remove code
 | |
| are known to have an adverse effect on debugging with source maps. This is
 | |
| expected as code is optimized and mappings are often simply not possible as
 | |
| some code no longer exists. For highest fidelity in source map debugging
 | |
| disable the `compress` option and just use `mangle`.
 | |
| 
 | |
| When debugging, make sure you enable the **"map scopes"** feature to map mangled variable names back to their original names.  
 | |
| Without this, all variable values will be `undefined`. See https://github.com/terser/terser/issues/1367 for more details.
 | |
| <br/><br/>
 | |
| 
 | |
| 
 | |
| 
 | |
| ### Compiler assumptions
 | |
| 
 | |
| To allow for better optimizations, the compiler makes various assumptions:
 | |
| 
 | |
| - `.toString()` and `.valueOf()` don't have side effects, and for built-in
 | |
|   objects they have not been overridden.
 | |
| - `undefined`, `NaN` and `Infinity` have not been externally redefined.
 | |
| - `arguments.callee`, `arguments.caller` and `Function.prototype.caller` are not used.
 | |
| - The code doesn't expect the contents of `Function.prototype.toString()` or
 | |
|   `Error.prototype.stack` to be anything in particular.
 | |
| - Getting and setting properties on a plain object does not cause other side effects
 | |
|   (using `.watch()` or `Proxy`).
 | |
| - Object properties can be added, removed and modified (not prevented with
 | |
|   `Object.defineProperty()`, `Object.defineProperties()`, `Object.freeze()`,
 | |
|   `Object.preventExtensions()` or `Object.seal()`).
 | |
| - `document.all` is not `== null`
 | |
| - Assigning properties to a class doesn't have side effects and does not throw.
 | |
| 
 | |
| ### Build Tools and Adaptors using Terser
 | |
| 
 | |
| https://www.npmjs.com/browse/depended/terser
 | |
| 
 | |
| ### Replacing `uglify-es` with `terser` in a project using `yarn`
 | |
| 
 | |
| A number of JS bundlers and uglify wrappers are still using buggy versions
 | |
| of `uglify-es` and have not yet upgraded to `terser`. If you are using `yarn`
 | |
| you can add the following alias to your project's `package.json` file:
 | |
| 
 | |
| ```js
 | |
|   "resolutions": {
 | |
|     "uglify-es": "npm:terser"
 | |
|   }
 | |
| ```
 | |
| 
 | |
| to use `terser` instead of `uglify-es` in all deeply nested dependencies
 | |
| without changing any code.
 | |
| 
 | |
| Note: for this change to take effect you must run the following commands
 | |
| to remove the existing `yarn` lock file and reinstall all packages:
 | |
| 
 | |
| ```
 | |
| $ rm -rf node_modules yarn.lock
 | |
| $ yarn
 | |
| ```
 | |
| 
 | |
| <!-- MISCELLANEOUS:END -->
 | |
| 
 | |
| # Reporting issues
 | |
| 
 | |
| <!-- REPORTING_ISSUES:START -->
 | |
| 
 | |
| ## A minimal, reproducible example
 | |
| 
 | |
| You're expected to provide a [minimal reproducible example] of input code that will demonstrate your issue.
 | |
| 
 | |
| To get to this example, you can remove bits of your code and stop if your issue ceases to reproduce.
 | |
| 
 | |
| ## Obtaining the source code given to Terser
 | |
| 
 | |
| Because users often don't control the call to `await minify()` or its arguments, Terser provides a `TERSER_DEBUG_DIR` environment variable to make terser output some debug logs.
 | |
| 
 | |
| These logs will contain the input code and options of each `minify()` call.
 | |
| 
 | |
| ```bash
 | |
| TERSER_DEBUG_DIR=/tmp/terser-log-dir command-that-uses-terser
 | |
| ls /tmp/terser-log-dir
 | |
| terser-debug-123456.log
 | |
| ```
 | |
| 
 | |
| If you're not sure how to set an environment variable on your shell (the above example works in bash), you can try using cross-env:
 | |
| 
 | |
| ```
 | |
| > npx cross-env TERSER_DEBUG_DIR=/path/to/logs command-that-uses-terser
 | |
| ```
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| 
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| ## Stack traces
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| 
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| In the terser CLI we use [source-map-support](https://npmjs.com/source-map-support) to produce good error stacks. In your own app, you're expected to enable source-map-support (read their docs) to have nice stack traces that will help you write good issues.
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| 
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| <!-- REPORTING_ISSUES:END -->
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| 
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| # README.md Patrons:
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| 
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| *note*: <s>You can support this project on patreon: [link]</s> **The Terser Patreon is shutting down in favor of opencollective**. Check out [PATRONS.md](https://github.com/terser/terser/blob/master/PATRONS.md) for our first-tier patrons.
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| 
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| These are the second-tier patrons. Great thanks for your support!
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| 
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|  * CKEditor 
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|  * 38elements 
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| 
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| ## Contributors
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| 
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| ### Code Contributors
 | |
| 
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| This project exists thanks to all the people who contribute. [[Contribute](CONTRIBUTING.md)].
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| <a href="https://github.com/terser/terser/graphs/contributors"><img src="https://opencollective.com/terser/contributors.svg?width=890&button=false" /></a>
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| 
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| ### Financial Contributors
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| 
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| Become a financial contributor and help us sustain our community. [[Contribute](https://opencollective.com/terser/contribute)]
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| 
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| #### Individuals
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| 
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| <a href="https://opencollective.com/terser"><img src="https://opencollective.com/terser/individuals.svg?width=890"></a>
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| 
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| #### Organizations
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| 
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| Support this project with your organization. Your logo will show up here with a link to your website. [[Contribute](https://opencollective.com/terser/contribute)]
 | |
| 
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| <a href="https://opencollective.com/terser/organization/0/website"><img src="https://opencollective.com/terser/organization/0/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/1/website"><img src="https://opencollective.com/terser/organization/1/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/2/website"><img src="https://opencollective.com/terser/organization/2/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/3/website"><img src="https://opencollective.com/terser/organization/3/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/4/website"><img src="https://opencollective.com/terser/organization/4/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/5/website"><img src="https://opencollective.com/terser/organization/5/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/6/website"><img src="https://opencollective.com/terser/organization/6/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/7/website"><img src="https://opencollective.com/terser/organization/7/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/8/website"><img src="https://opencollective.com/terser/organization/8/avatar.svg"></a>
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| <a href="https://opencollective.com/terser/organization/9/website"><img src="https://opencollective.com/terser/organization/9/avatar.svg"></a>
 |