1 | UglifyJS 3
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2 | ==========
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3 |
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4 | UglifyJS is a JavaScript parser, minifier, compressor and beautifier toolkit.
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5 |
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6 | #### Note:
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7 | - `uglify-js` supports JavaScript and most language features in ECMAScript.
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8 | - For more exotic parts of ECMAScript, process your source file with transpilers
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9 | like [Babel](https://babeljs.io/) before passing onto `uglify-js`.
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10 | - `uglify-js@3` has a simplified [API](#api-reference) and [CLI](#command-line-usage)
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11 | that is not backwards compatible with [`uglify-js@2`](https://github.com/mishoo/UglifyJS/tree/v2.x).
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12 |
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13 | Install
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14 | -------
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15 |
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16 | First make sure you have installed the latest version of [node.js](http://nodejs.org/)
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17 | (You may need to restart your computer after this step).
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18 |
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19 | From NPM for use as a command line app:
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20 |
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21 | npm install uglify-js -g
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22 |
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23 | From NPM for programmatic use:
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24 |
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25 | npm install uglify-js
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26 |
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27 | # Command line usage
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28 |
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29 | uglifyjs [input files] [options]
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30 |
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31 | UglifyJS can take multiple input files. It's recommended that you pass the
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32 | input files first, then pass the options. UglifyJS will parse input files
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33 | in sequence and apply any compression options. The files are parsed in the
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34 | same global scope, that is, a reference from a file to some
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35 | variable/function declared in another file will be matched properly.
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36 |
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37 | If no input file is specified, UglifyJS will read from STDIN.
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38 |
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39 | If you wish to pass your options before the input files, separate the two with
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40 | a double dash to prevent input files being used as option arguments:
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41 |
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42 | uglifyjs --compress --mangle -- input.js
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43 |
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44 | ### Command line options
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45 |
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46 | ```
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47 | -h, --help Print usage information.
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48 | `--help options` for details on available options.
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49 | -V, --version Print version number.
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50 | -p, --parse <options> Specify parser options:
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51 | `acorn` Use Acorn for parsing.
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52 | `bare_returns` Allow return outside of functions.
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53 | Useful when minifying CommonJS
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54 | modules and Userscripts that may
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55 | be anonymous function wrapped (IIFE)
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56 | by the .user.js engine `caller`.
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57 | `expression` Parse a single expression, rather than
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58 | a program (for parsing JSON).
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59 | `spidermonkey` Assume input files are SpiderMonkey
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60 | AST format (as JSON).
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61 | -c, --compress [options] Enable compressor/specify compressor options:
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62 | `pure_funcs` List of functions that can be safely
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63 | removed when their return values are
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64 | not used.
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65 | -m, --mangle [options] Mangle names/specify mangler options:
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66 | `reserved` List of names that should not be mangled.
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67 | --mangle-props [options] Mangle properties/specify mangler options:
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68 | `builtins` Mangle property names that overlaps
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69 | with standard JavaScript globals.
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70 | `debug` Add debug prefix and suffix.
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71 | `domprops` Mangle property names that overlaps
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72 | with DOM properties.
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73 | `keep_quoted` Only mangle unquoted properties.
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74 | `regex` Only mangle matched property names.
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75 | `reserved` List of names that should not be mangled.
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76 | -b, --beautify [options] Beautify output/specify output options:
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77 | `beautify` Enabled with `--beautify` by default.
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78 | `preamble` Preamble to prepend to the output. You
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79 | can use this to insert a comment, for
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80 | example for licensing information.
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81 | This will not be parsed, but the source
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82 | map will adjust for its presence.
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83 | `quote_style` Quote style:
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84 | 0 - auto
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85 | 1 - single
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86 | 2 - double
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87 | 3 - original
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88 | `wrap_iife` Wrap IIFEs in parentheses. Note: you may
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89 | want to disable `negate_iife` under
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90 | compressor options.
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91 | -O, --output-opts [options] Specify output options (`beautify` disabled by default).
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92 | -o, --output <file> Output file path (default STDOUT). Specify `ast` or
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93 | `spidermonkey` to write UglifyJS or SpiderMonkey AST
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94 | as JSON to STDOUT respectively.
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95 | --annotations Process and preserve comment annotations.
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96 | (`/*@__PURE__*/` or `/*#__PURE__*/`)
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97 | --no-annotations Ignore and discard comment annotations.
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98 | --comments [filter] Preserve copyright comments in the output. By
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99 | default this works like Google Closure, keeping
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100 | JSDoc-style comments that contain "@license" or
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101 | "@preserve". You can optionally pass one of the
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102 | following arguments to this flag:
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103 | - "all" to keep all comments
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104 | - a valid JS RegExp like `/foo/` or `/^!/` to
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105 | keep only matching comments.
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106 | Note that currently not *all* comments can be
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107 | kept when compression is on, because of dead
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108 | code removal or cascading statements into
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109 | sequences.
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110 | --config-file <file> Read `minify()` options from JSON file.
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111 | -d, --define <expr>[=value] Global definitions.
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112 | -e, --enclose [arg[:value]] Embed everything in a big function, with configurable
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113 | argument(s) & value(s).
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114 | --ie8 Support non-standard Internet Explorer 8.
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115 | Equivalent to setting `ie8: true` in `minify()`
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116 | for `compress`, `mangle` and `output` options.
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117 | By default UglifyJS will not try to be IE-proof.
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118 | --keep-fnames Do not mangle/drop function names. Useful for
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119 | code relying on Function.prototype.name.
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120 | --name-cache <file> File to hold mangled name mappings.
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121 | --self Build UglifyJS as a library (implies --wrap UglifyJS)
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122 | --source-map [options] Enable source map/specify source map options:
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123 | `base` Path to compute relative paths from input files.
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124 | `content` Input source map, useful if you're compressing
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125 | JS that was generated from some other original
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126 | code. Specify "inline" if the source map is
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127 | included within the sources.
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128 | `filename` Filename and/or location of the output source
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129 | (sets `file` attribute in source map).
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130 | `includeSources` Pass this flag if you want to include
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131 | the content of source files in the
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132 | source map as sourcesContent property.
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133 | `names` Include symbol names in the source map.
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134 | `root` Path to the original source to be included in
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135 | the source map.
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136 | `url` If specified, path to the source map to append in
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137 | `//# sourceMappingURL`.
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138 | --timings Display operations run time on STDERR.
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139 | --toplevel Compress and/or mangle variables in top level scope.
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140 | --v8 Support non-standard Chrome & Node.js
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141 | Equivalent to setting `v8: true` in `minify()`
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142 | for `mangle` and `output` options.
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143 | By default UglifyJS will not try to be v8-proof.
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144 | --verbose Print diagnostic messages.
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145 | --warn Print warning messages.
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146 | --webkit Support non-standard Safari/Webkit.
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147 | Equivalent to setting `webkit: true` in `minify()`
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148 | for `mangle` and `output` options.
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149 | By default UglifyJS will not try to be Safari-proof.
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150 | --wrap <name> Embed everything in a big function, making the
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151 | “exports” and “global” variables available. You
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152 | need to pass an argument to this option to
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153 | specify the name that your module will take
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154 | when included in, say, a browser.
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155 | ```
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156 |
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157 | Specify `--output` (`-o`) to declare the output file. Otherwise the output
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158 | goes to STDOUT.
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159 |
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160 | ## CLI source map options
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161 |
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162 | UglifyJS can generate a source map file, which is highly useful for
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163 | debugging your compressed JavaScript. To get a source map, pass
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164 | `--source-map --output output.js` (source map will be written out to
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165 | `output.js.map`).
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166 |
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167 | Additional options:
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168 |
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169 | - `--source-map "filename='<NAME>'"` to specify the name of the source map. The value of
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170 | `filename` is only used to set `file` attribute (see [the spec][sm-spec])
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171 | in source map file.
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172 |
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173 | - `--source-map "root='<URL>'"` to pass the URL where the original files can be found.
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174 |
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175 | - `--source-map "names=false"` to omit symbol names if you want to reduce size
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176 | of the source map file.
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177 |
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178 | - `--source-map "url='<URL>'"` to specify the URL where the source map can be found.
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179 | Otherwise UglifyJS assumes HTTP `X-SourceMap` is being used and will omit the
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180 | `//# sourceMappingURL=` directive.
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181 |
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182 | For example:
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183 |
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184 | uglifyjs js/file1.js js/file2.js \
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185 | -o foo.min.js -c -m \
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186 | --source-map "root='http://foo.com/src',url='foo.min.js.map'"
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187 |
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188 | The above will compress and mangle `file1.js` and `file2.js`, will drop the
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189 | output in `foo.min.js` and the source map in `foo.min.js.map`. The source
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190 | mapping will refer to `http://foo.com/src/js/file1.js` and
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191 | `http://foo.com/src/js/file2.js` (in fact it will list `http://foo.com/src`
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192 | as the source map root, and the original files as `js/file1.js` and
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193 | `js/file2.js`).
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194 |
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195 | ### Composed source map
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196 |
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197 | When you're compressing JS code that was output by a compiler such as
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198 | CoffeeScript, mapping to the JS code won't be too helpful. Instead, you'd
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199 | like to map back to the original code (i.e. CoffeeScript). UglifyJS has an
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200 | option to take an input source map. Assuming you have a mapping from
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201 | CoffeeScript → compiled JS, UglifyJS can generate a map from CoffeeScript →
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202 | compressed JS by mapping every token in the compiled JS to its original
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203 | location.
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204 |
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205 | To use this feature pass `--source-map "content='/path/to/input/source.map'"`
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206 | or `--source-map "content=inline"` if the source map is included inline with
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207 | the sources.
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208 |
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209 | ## CLI compress options
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210 |
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211 | You need to pass `--compress` (`-c`) to enable the compressor. Optionally
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212 | you can pass a comma-separated list of [compress options](#compress-options).
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213 |
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214 | Options are in the form `foo=bar`, or just `foo` (the latter implies
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215 | a boolean option that you want to set `true`; it's effectively a
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216 | shortcut for `foo=true`).
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217 |
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218 | Example:
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219 |
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220 | uglifyjs file.js -c toplevel,sequences=false
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221 |
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222 | ## CLI mangle options
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223 |
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224 | To enable the mangler you need to pass `--mangle` (`-m`). The following
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225 | (comma-separated) options are supported:
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226 |
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227 | - `eval` (default: `false`) — mangle names visible in scopes where `eval` or
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228 | `with` are used.
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229 |
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230 | - `reserved` (default: `[]`) — when mangling is enabled but you want to
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231 | prevent certain names from being mangled, you can declare those names with
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232 | `--mangle reserved` — pass a comma-separated list of names. For example:
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233 |
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234 | uglifyjs ... -m reserved=['$','require','exports']
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235 |
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236 | to prevent the `require`, `exports` and `$` names from being changed.
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237 |
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238 | ### CLI mangling property names (`--mangle-props`)
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239 |
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240 | **Note:** THIS WILL PROBABLY BREAK YOUR CODE. Mangling property names
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241 | is a separate step, different from variable name mangling. Pass
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242 | `--mangle-props` to enable it. It will mangle all properties in the
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243 | input code with the exception of built in DOM properties and properties
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244 | in core JavaScript classes. For example:
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245 |
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246 | ```javascript
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247 | // example.js
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248 | var x = {
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249 | baz_: 0,
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250 | foo_: 1,
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251 | calc: function() {
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252 | return this.foo_ + this.baz_;
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253 | }
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254 | };
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255 | x.bar_ = 2;
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256 | x["baz_"] = 3;
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257 | console.log(x.calc());
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258 | ```
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259 | Mangle all properties (except for JavaScript `builtins`):
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260 | ```bash
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261 | $ uglifyjs example.js -c -m --mangle-props
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262 | ```
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263 | ```javascript
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264 | var x={o:0,_:1,l:function(){return this._+this.o}};x.t=2,x.o=3,console.log(x.l());
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265 | ```
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266 | Mangle all properties except for `reserved` properties:
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267 | ```bash
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268 | $ uglifyjs example.js -c -m --mangle-props reserved=[foo_,bar_]
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269 | ```
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270 | ```javascript
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271 | var x={o:0,foo_:1,_:function(){return this.foo_+this.o}};x.bar_=2,x.o=3,console.log(x._());
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272 | ```
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273 | Mangle all properties matching a `regex`:
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274 | ```bash
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275 | $ uglifyjs example.js -c -m --mangle-props regex=/_$/
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276 | ```
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277 | ```javascript
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278 | var x={o:0,_:1,calc:function(){return this._+this.o}};x.l=2,x.o=3,console.log(x.calc());
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279 | ```
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280 |
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281 | Combining mangle properties options:
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282 | ```bash
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283 | $ uglifyjs example.js -c -m --mangle-props regex=/_$/,reserved=[bar_]
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284 | ```
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285 | ```javascript
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286 | var x={o:0,_:1,calc:function(){return this._+this.o}};x.bar_=2,x.o=3,console.log(x.calc());
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287 | ```
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288 |
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289 | In order for this to be of any use, we avoid mangling standard JS names by
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290 | default (`--mangle-props builtins` to override).
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291 |
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292 | A default exclusion file is provided in `tools/domprops.json` which should
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293 | cover most standard JS and DOM properties defined in various browsers. Pass
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294 | `--mangle-props domprops` to disable this feature.
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295 |
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296 | A regular expression can be used to define which property names should be
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297 | mangled. For example, `--mangle-props regex=/^_/` will only mangle property
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298 | names that start with an underscore.
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299 |
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300 | When you compress multiple files using this option, in order for them to
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301 | work together in the end we need to ensure somehow that one property gets
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302 | mangled to the same name in all of them. For this, pass `--name-cache filename.json`
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303 | and UglifyJS will maintain these mappings in a file which can then be reused.
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304 | It should be initially empty. Example:
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305 |
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306 | ```bash
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307 | $ rm -f /tmp/cache.json # start fresh
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308 | $ uglifyjs file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js
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309 | $ uglifyjs file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js
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310 | ```
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311 |
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312 | Now, `part1.js` and `part2.js` will be consistent with each other in terms
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313 | of mangled property names.
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314 |
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315 | Using the name cache is not necessary if you compress all your files in a
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316 | single call to UglifyJS.
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317 |
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318 | ### Mangling unquoted names (`--mangle-props keep_quoted`)
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319 |
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320 | Using quoted property name (`o["foo"]`) reserves the property name (`foo`)
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321 | so that it is not mangled throughout the entire script even when used in an
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322 | unquoted style (`o.foo`). Example:
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323 |
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324 | ```javascript
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325 | // stuff.js
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326 | var o = {
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327 | "foo": 1,
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328 | bar: 3
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329 | };
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330 | o.foo += o.bar;
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331 | console.log(o.foo);
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332 | ```
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333 | ```bash
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334 | $ uglifyjs stuff.js --mangle-props keep_quoted -c -m
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335 | ```
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336 | ```javascript
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337 | var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo);
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338 | ```
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339 |
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340 | ### Debugging property name mangling
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341 |
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342 | You can also pass `--mangle-props debug` in order to mangle property names
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343 | without completely obscuring them. For example the property `o.foo`
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344 | would mangle to `o._$foo$_` with this option. This allows property mangling
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345 | of a large codebase while still being able to debug the code and identify
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346 | where mangling is breaking things.
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347 |
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348 | ```bash
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349 | $ uglifyjs stuff.js --mangle-props debug -c -m
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350 | ```
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351 | ```javascript
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352 | var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_);
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353 | ```
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354 |
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355 | You can also pass a custom suffix using `--mangle-props debug=XYZ`. This would then
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356 | mangle `o.foo` to `o._$foo$XYZ_`. You can change this each time you compile a
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357 | script to identify how a property got mangled. One technique is to pass a
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358 | random number on every compile to simulate mangling changing with different
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359 | inputs (e.g. as you update the input script with new properties), and to help
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360 | identify mistakes like writing mangled keys to storage.
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361 |
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362 |
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363 | # API Reference
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364 |
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365 | Assuming installation via NPM, you can load UglifyJS in your application
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366 | like this:
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367 | ```javascript
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368 | var UglifyJS = require("uglify-js");
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369 | ```
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370 |
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371 | There is a single high level function, **`minify(code, options)`**,
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372 | which will perform all minification [phases](#minify-options) in a configurable
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373 | manner. By default `minify()` will enable the options [`compress`](#compress-options)
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374 | and [`mangle`](#mangle-options). Example:
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375 | ```javascript
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376 | var code = "function add(first, second) { return first + second; }";
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377 | var result = UglifyJS.minify(code);
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378 | console.log(result.error); // runtime error, or `undefined` if no error
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379 | console.log(result.code); // minified output: function add(n,d){return n+d}
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380 | ```
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381 |
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382 | You can `minify` more than one JavaScript file at a time by using an object
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383 | for the first argument where the keys are file names and the values are source
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384 | code:
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385 | ```javascript
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386 | var code = {
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387 | "file1.js": "function add(first, second) { return first + second; }",
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388 | "file2.js": "console.log(add(1 + 2, 3 + 4));"
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389 | };
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390 | var result = UglifyJS.minify(code);
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391 | console.log(result.code);
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392 | // function add(d,n){return d+n}console.log(add(3,7));
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393 | ```
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394 |
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395 | The `toplevel` option:
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396 | ```javascript
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397 | var code = {
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398 | "file1.js": "function add(first, second) { return first + second; }",
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399 | "file2.js": "console.log(add(1 + 2, 3 + 4));"
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400 | };
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401 | var options = { toplevel: true };
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402 | var result = UglifyJS.minify(code, options);
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403 | console.log(result.code);
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404 | // console.log(3+7);
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405 | ```
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406 |
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407 | The `nameCache` option:
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408 | ```javascript
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409 | var options = {
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410 | mangle: {
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411 | toplevel: true,
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412 | },
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413 | nameCache: {}
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414 | };
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415 | var result1 = UglifyJS.minify({
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416 | "file1.js": "function add(first, second) { return first + second; }"
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417 | }, options);
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418 | var result2 = UglifyJS.minify({
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419 | "file2.js": "console.log(add(1 + 2, 3 + 4));"
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420 | }, options);
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421 | console.log(result1.code);
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422 | // function n(n,r){return n+r}
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423 | console.log(result2.code);
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424 | // console.log(n(3,7));
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425 | ```
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426 |
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427 | You may persist the name cache to the file system in the following way:
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428 | ```javascript
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429 | var cacheFileName = "/tmp/cache.json";
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430 | var options = {
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431 | mangle: {
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432 | properties: true,
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433 | },
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434 | nameCache: JSON.parse(fs.readFileSync(cacheFileName, "utf8"))
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435 | };
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436 | fs.writeFileSync("part1.js", UglifyJS.minify({
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437 | "file1.js": fs.readFileSync("file1.js", "utf8"),
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438 | "file2.js": fs.readFileSync("file2.js", "utf8")
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439 | }, options).code, "utf8");
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440 | fs.writeFileSync("part2.js", UglifyJS.minify({
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441 | "file3.js": fs.readFileSync("file3.js", "utf8"),
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442 | "file4.js": fs.readFileSync("file4.js", "utf8")
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443 | }, options).code, "utf8");
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444 | fs.writeFileSync(cacheFileName, JSON.stringify(options.nameCache), "utf8");
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445 | ```
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446 |
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447 | An example of a combination of `minify()` options:
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448 | ```javascript
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449 | var code = {
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450 | "file1.js": "function add(first, second) { return first + second; }",
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451 | "file2.js": "console.log(add(1 + 2, 3 + 4));"
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452 | };
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453 | var options = {
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454 | toplevel: true,
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455 | compress: {
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456 | global_defs: {
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457 | "@console.log": "alert"
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458 | },
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459 | passes: 2
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460 | },
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461 | output: {
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462 | beautify: false,
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463 | preamble: "/* uglified */"
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464 | }
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465 | };
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466 | var result = UglifyJS.minify(code, options);
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467 | console.log(result.code);
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468 | // /* uglified */
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469 | // alert(10);"
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470 | ```
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471 |
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472 | To produce warnings:
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473 | ```javascript
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474 | var code = "function f(){ var u; return 2 + 3; }";
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475 | var options = { warnings: true };
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476 | var result = UglifyJS.minify(code, options);
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477 | console.log(result.error); // runtime error, `undefined` in this case
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478 | console.log(result.warnings); // [ 'Dropping unused variable u [0:1,18]' ]
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479 | console.log(result.code); // function f(){return 5}
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480 | ```
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481 |
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482 | An error example:
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483 | ```javascript
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484 | var result = UglifyJS.minify({"foo.js" : "if (0) else console.log(1);"});
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485 | console.log(JSON.stringify(result.error));
|
486 | // {"message":"Unexpected token: keyword (else)","filename":"foo.js","line":1,"col":7,"pos":7}
|
487 | ```
|
488 | Note: unlike `uglify-js@2.x`, the `3.x` API does not throw errors. To
|
489 | achieve a similar effect one could do the following:
|
490 | ```javascript
|
491 | var result = UglifyJS.minify(code, options);
|
492 | if (result.error) throw result.error;
|
493 | ```
|
494 |
|
495 | ## Minify options
|
496 |
|
497 | - `annotations` — pass `false` to ignore all comment annotations and elide them
|
498 | from output. Useful when, for instance, external tools incorrectly applied
|
499 | `/*@__PURE__*/` or `/*#__PURE__*/`. Pass `true` to both compress and retain
|
500 | comment annotations in output to allow for further processing downstream.
|
501 |
|
502 | - `compress` (default: `{}`) — pass `false` to skip compressing entirely.
|
503 | Pass an object to specify custom [compress options](#compress-options).
|
504 |
|
505 | - `ie8` (default: `false`) — set to `true` to support IE8.
|
506 |
|
507 | - `keep_fnames` (default: `false`) — pass `true` to prevent discarding or mangling
|
508 | of function names. Useful for code relying on `Function.prototype.name`.
|
509 |
|
510 | - `mangle` (default: `true`) — pass `false` to skip mangling names, or pass
|
511 | an object to specify [mangle options](#mangle-options) (see below).
|
512 |
|
513 | - `mangle.properties` (default: `false`) — a subcategory of the mangle option.
|
514 | Pass an object to specify custom [mangle property options](#mangle-properties-options).
|
515 |
|
516 | - `nameCache` (default: `null`) — pass an empty object `{}` or a previously
|
517 | used `nameCache` object if you wish to cache mangled variable and
|
518 | property names across multiple invocations of `minify()`. Note: this is
|
519 | a read/write property. `minify()` will read the name cache state of this
|
520 | object and update it during minification so that it may be
|
521 | reused or externally persisted by the user.
|
522 |
|
523 | - `output` (default: `null`) — pass an object if you wish to specify
|
524 | additional [output options](#output-options). The defaults are optimized
|
525 | for best compression.
|
526 |
|
527 | - `parse` (default: `{}`) — pass an object if you wish to specify some
|
528 | additional [parse options](#parse-options).
|
529 |
|
530 | - `sourceMap` (default: `false`) — pass an object if you wish to specify
|
531 | [source map options](#source-map-options).
|
532 |
|
533 | - `toplevel` (default: `false`) — set to `true` if you wish to enable top level
|
534 | variable and function name mangling and to drop unused variables and functions.
|
535 |
|
536 | - `v8` (default: `false`) — enable workarounds for Chrome & Node.js bugs.
|
537 |
|
538 | - `warnings` (default: `false`) — pass `true` to return compressor warnings
|
539 | in `result.warnings`. Use the value `"verbose"` for more detailed warnings.
|
540 |
|
541 | - `webkit` (default: `false`) — enable workarounds for Safari/WebKit bugs.
|
542 | PhantomJS users should set this option to `true`.
|
543 |
|
544 | ## Minify options structure
|
545 |
|
546 | ```javascript
|
547 | {
|
548 | parse: {
|
549 | // parse options
|
550 | },
|
551 | compress: {
|
552 | // compress options
|
553 | },
|
554 | mangle: {
|
555 | // mangle options
|
556 |
|
557 | properties: {
|
558 | // mangle property options
|
559 | }
|
560 | },
|
561 | output: {
|
562 | // output options
|
563 | },
|
564 | sourceMap: {
|
565 | // source map options
|
566 | },
|
567 | nameCache: null, // or specify a name cache object
|
568 | toplevel: false,
|
569 | ie8: false,
|
570 | warnings: false,
|
571 | }
|
572 | ```
|
573 |
|
574 | ### Source map options
|
575 |
|
576 | To generate a source map:
|
577 | ```javascript
|
578 | var result = UglifyJS.minify({"file1.js": "var a = function() {};"}, {
|
579 | sourceMap: {
|
580 | filename: "out.js",
|
581 | url: "out.js.map"
|
582 | }
|
583 | });
|
584 | console.log(result.code); // minified output
|
585 | console.log(result.map); // source map
|
586 | ```
|
587 |
|
588 | Note that the source map is not saved in a file, it's just returned in
|
589 | `result.map`. The value passed for `sourceMap.url` is only used to set
|
590 | `//# sourceMappingURL=out.js.map` in `result.code`. The value of
|
591 | `filename` is only used to set `file` attribute (see [the spec][sm-spec])
|
592 | in source map file.
|
593 |
|
594 | You can set option `sourceMap.url` to be `"inline"` and source map will
|
595 | be appended to code.
|
596 |
|
597 | You can also specify sourceRoot property to be included in source map:
|
598 | ```javascript
|
599 | var result = UglifyJS.minify({"file1.js": "var a = function() {};"}, {
|
600 | sourceMap: {
|
601 | root: "http://example.com/src",
|
602 | url: "out.js.map"
|
603 | }
|
604 | });
|
605 | ```
|
606 |
|
607 | If you're compressing compiled JavaScript and have a source map for it, you
|
608 | can use `sourceMap.content`:
|
609 | ```javascript
|
610 | var result = UglifyJS.minify({"compiled.js": "compiled code"}, {
|
611 | sourceMap: {
|
612 | content: "content from compiled.js.map",
|
613 | url: "minified.js.map"
|
614 | }
|
615 | });
|
616 | // same as before, it returns `code` and `map`
|
617 | ```
|
618 |
|
619 | If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.url`.
|
620 |
|
621 | If you wish to reduce file size of the source map, set option `sourceMap.names`
|
622 | to be `false` and all symbol names will be omitted.
|
623 |
|
624 | ## Parse options
|
625 |
|
626 | - `bare_returns` (default: `false`) — support top level `return` statements
|
627 |
|
628 | - `html5_comments` (default: `true`)
|
629 |
|
630 | - `shebang` (default: `true`) — support `#!command` as the first line
|
631 |
|
632 | ## Compress options
|
633 |
|
634 | - `annotations` (default: `true`) — Pass `false` to disable potentially dropping
|
635 | functions marked as "pure". A function call is marked as "pure" if a comment
|
636 | annotation `/*@__PURE__*/` or `/*#__PURE__*/` immediately precedes the call. For
|
637 | example: `/*@__PURE__*/foo();`
|
638 |
|
639 | - `arguments` (default: `true`) — replace `arguments[index]` with function
|
640 | parameter name whenever possible.
|
641 |
|
642 | - `arrows` (default: `true`) — apply optimizations to arrow functions
|
643 |
|
644 | - `assignments` (default: `true`) — apply optimizations to assignment expressions
|
645 |
|
646 | - `awaits` (default: `true`) — apply optimizations to `await` expressions
|
647 |
|
648 | - `booleans` (default: `true`) — various optimizations for boolean context,
|
649 | for example `!!a ? b : c → a ? b : c`
|
650 |
|
651 | - `collapse_vars` (default: `true`) — Collapse single-use non-constant variables,
|
652 | side effects permitting.
|
653 |
|
654 | - `comparisons` (default: `true`) — apply certain optimizations to binary nodes,
|
655 | e.g. `!(a <= b) → a > b`, attempts to negate binary nodes, e.g.
|
656 | `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc.
|
657 |
|
658 | - `conditionals` (default: `true`) — apply optimizations for `if`-s and conditional
|
659 | expressions
|
660 |
|
661 | - `dead_code` (default: `true`) — remove unreachable code
|
662 |
|
663 | - `default_values` (default: `true`) — drop overshadowed default values
|
664 |
|
665 | - `directives` (default: `true`) — remove redundant or non-standard directives
|
666 |
|
667 | - `drop_console` (default: `false`) — Pass `true` to discard calls to
|
668 | `console.*` functions. If you wish to drop a specific function call
|
669 | such as `console.info` and/or retain side effects from function arguments
|
670 | after dropping the function call then use `pure_funcs` instead.
|
671 |
|
672 | - `drop_debugger` (default: `true`) — remove `debugger;` statements
|
673 |
|
674 | - `evaluate` (default: `true`) — Evaluate expression for shorter constant
|
675 | representation. Pass `"eager"` to always replace function calls whenever
|
676 | possible, or a positive integer to specify an upper bound for each individual
|
677 | evaluation in number of characters.
|
678 |
|
679 | - `expression` (default: `false`) — Pass `true` to preserve completion values
|
680 | from terminal statements without `return`, e.g. in bookmarklets.
|
681 |
|
682 | - `functions` (default: `true`) — convert declarations from `var` to `function`
|
683 | whenever possible.
|
684 |
|
685 | - `global_defs` (default: `{}`) — see [conditional compilation](#conditional-compilation)
|
686 |
|
687 | - `hoist_exports` (default: `true`) — hoist `export` statements to facilitate
|
688 | various `compress` and `mangle` optimizations.
|
689 |
|
690 | - `hoist_funs` (default: `false`) — hoist function declarations
|
691 |
|
692 | - `hoist_props` (default: `true`) — hoist properties from constant object and
|
693 | array literals into regular variables subject to a set of constraints. For example:
|
694 | `var o={p:1, q:2}; f(o.p, o.q);` is converted to `f(1, 2);`. Note: `hoist_props`
|
695 | works best with `toplevel` and `mangle` enabled, alongside with `compress` option
|
696 | `passes` set to `2` or higher.
|
697 |
|
698 | - `hoist_vars` (default: `false`) — hoist `var` declarations (this is `false`
|
699 | by default because it seems to increase the size of the output in general)
|
700 |
|
701 | - `if_return` (default: `true`) — optimizations for if/return and if/continue
|
702 |
|
703 | - `imports` (default: `true`) — drop unreferenced import symbols when used with `unused`
|
704 |
|
705 | - `inline` (default: `true`) — inline calls to function with simple/`return` statement:
|
706 | - `false` — same as `0`
|
707 | - `0` — disabled inlining
|
708 | - `1` — inline simple functions
|
709 | - `2` — inline functions with arguments
|
710 | - `3` — inline functions with arguments and variables
|
711 | - `true` — same as `3`
|
712 |
|
713 | - `join_vars` (default: `true`) — join consecutive `var` statements
|
714 |
|
715 | - `keep_fargs` (default: `false`) — discard unused function arguments except
|
716 | when unsafe to do so, e.g. code which relies on `Function.prototype.length`.
|
717 | Pass `true` to always retain function arguments.
|
718 |
|
719 | - `keep_infinity` (default: `false`) — Pass `true` to prevent `Infinity` from
|
720 | being compressed into `1/0`, which may cause performance issues on Chrome.
|
721 |
|
722 | - `loops` (default: `true`) — optimizations for `do`, `while` and `for` loops
|
723 | when we can statically determine the condition.
|
724 |
|
725 | - `merge_vars` (default: `true`) — combine and reuse variables.
|
726 |
|
727 | - `negate_iife` (default: `true`) — negate "Immediately-Called Function Expressions"
|
728 | where the return value is discarded, to avoid the parens that the
|
729 | code generator would insert.
|
730 |
|
731 | - `objects` (default: `true`) — compact duplicate keys in object literals.
|
732 |
|
733 | - `passes` (default: `1`) — The maximum number of times to run compress.
|
734 | In some cases more than one pass leads to further compressed code. Keep in
|
735 | mind more passes will take more time.
|
736 |
|
737 | - `properties` (default: `true`) — rewrite property access using the dot notation, for
|
738 | example `foo["bar"] → foo.bar`
|
739 |
|
740 | - `pure_funcs` (default: `null`) — You can pass an array of names and
|
741 | UglifyJS will assume that those functions do not produce side
|
742 | effects. DANGER: will not check if the name is redefined in scope.
|
743 | An example case here, for instance `var q = Math.floor(a/b)`. If
|
744 | variable `q` is not used elsewhere, UglifyJS will drop it, but will
|
745 | still keep the `Math.floor(a/b)`, not knowing what it does. You can
|
746 | pass `pure_funcs: [ 'Math.floor' ]` to let it know that this
|
747 | function won't produce any side effect, in which case the whole
|
748 | statement would get discarded. The current implementation adds some
|
749 | overhead (compression will be slower). Make sure symbols under `pure_funcs`
|
750 | are also under `mangle.reserved` to avoid mangling.
|
751 |
|
752 | - `pure_getters` (default: `"strict"`) — If you pass `true` for
|
753 | this, UglifyJS will assume that object property access
|
754 | (e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects.
|
755 | Specify `"strict"` to treat `foo.bar` as side-effect-free only when
|
756 | `foo` is certain to not throw, i.e. not `null` or `undefined`.
|
757 |
|
758 | - `reduce_funcs` (default: `true`) — Allows single-use functions to be
|
759 | inlined as function expressions when permissible allowing further
|
760 | optimization. Enabled by default. Option depends on `reduce_vars`
|
761 | being enabled. Some code runs faster in the Chrome V8 engine if this
|
762 | option is disabled. Does not negatively impact other major browsers.
|
763 |
|
764 | - `reduce_vars` (default: `true`) — Improve optimization on variables assigned with and
|
765 | used as constant values.
|
766 |
|
767 | - `rests` (default: `true`) — apply optimizations to rest parameters
|
768 |
|
769 | - `sequences` (default: `true`) — join consecutive simple statements using the
|
770 | comma operator. May be set to a positive integer to specify the maximum number
|
771 | of consecutive comma sequences that will be generated. If this option is set to
|
772 | `true` then the default `sequences` limit is `200`. Set option to `false` or `0`
|
773 | to disable. The smallest `sequences` length is `2`. A `sequences` value of `1`
|
774 | is grandfathered to be equivalent to `true` and as such means `200`. On rare
|
775 | occasions the default sequences limit leads to very slow compress times in which
|
776 | case a value of `20` or less is recommended.
|
777 |
|
778 | - `side_effects` (default: `true`) — drop extraneous code which does not affect
|
779 | outcome of runtime execution.
|
780 |
|
781 | - `spreads` (default: `true`) — flatten spread expressions.
|
782 |
|
783 | - `strings` (default: `true`) — compact string concatenations.
|
784 |
|
785 | - `switches` (default: `true`) — de-duplicate and remove unreachable `switch` branches
|
786 |
|
787 | - `templates` (default: `true`) — compact template literals by embedding expressions
|
788 | and/or converting to string literals, e.g. `` `foo ${42}` → "foo 42"``
|
789 |
|
790 | - `top_retain` (default: `null`) — prevent specific toplevel functions and
|
791 | variables from `unused` removal (can be array, comma-separated, RegExp or
|
792 | function. Implies `toplevel`)
|
793 |
|
794 | - `toplevel` (default: `false`) — drop unreferenced functions (`"funcs"`) and/or
|
795 | variables (`"vars"`) in the top level scope (`false` by default, `true` to drop
|
796 | both unreferenced functions and variables)
|
797 |
|
798 | - `typeofs` (default: `true`) — Transforms `typeof foo == "undefined"` into
|
799 | `foo === void 0`. Note: recommend to set this value to `false` for IE10 and
|
800 | earlier versions due to known issues.
|
801 |
|
802 | - `unsafe` (default: `false`) — apply "unsafe" transformations (discussion below)
|
803 |
|
804 | - `unsafe_comps` (default: `false`) — compress expressions like `a <= b` assuming
|
805 | none of the operands can be (coerced to) `NaN`.
|
806 |
|
807 | - `unsafe_Function` (default: `false`) — compress and mangle `Function(args, code)`
|
808 | when both `args` and `code` are string literals.
|
809 |
|
810 | - `unsafe_math` (default: `false`) — optimize numerical expressions like
|
811 | `2 * x * 3` into `6 * x`, which may give imprecise floating point results.
|
812 |
|
813 | - `unsafe_proto` (default: `false`) — optimize expressions like
|
814 | `Array.prototype.slice.call(a)` into `[].slice.call(a)`
|
815 |
|
816 | - `unsafe_regexp` (default: `false`) — enable substitutions of variables with
|
817 | `RegExp` values the same way as if they are constants.
|
818 |
|
819 | - `unsafe_undefined` (default: `false`) — substitute `void 0` if there is a
|
820 | variable named `undefined` in scope (variable name will be mangled, typically
|
821 | reduced to a single character)
|
822 |
|
823 | - `unused` (default: `true`) — drop unreferenced functions and variables (simple
|
824 | direct variable assignments do not count as references unless set to `"keep_assign"`)
|
825 |
|
826 | - `varify` (default: `true`) — convert block-scoped declaractions into `var`
|
827 | whenever safe to do so
|
828 |
|
829 | - `yields` (default: `true`) — apply optimizations to `yield` expressions
|
830 |
|
831 | ## Mangle options
|
832 |
|
833 | - `eval` (default: `false`) — Pass `true` to mangle names visible in scopes
|
834 | where `eval` or `with` are used.
|
835 |
|
836 | - `reserved` (default: `[]`) — Pass an array of identifiers that should be
|
837 | excluded from mangling. Example: `["foo", "bar"]`.
|
838 |
|
839 | - `toplevel` (default: `false`) — Pass `true` to mangle names declared in the
|
840 | top level scope.
|
841 |
|
842 | Examples:
|
843 |
|
844 | ```javascript
|
845 | // test.js
|
846 | var globalVar;
|
847 | function funcName(firstLongName, anotherLongName) {
|
848 | var myVariable = firstLongName + anotherLongName;
|
849 | }
|
850 | ```
|
851 | ```javascript
|
852 | var code = fs.readFileSync("test.js", "utf8");
|
853 |
|
854 | UglifyJS.minify(code).code;
|
855 | // 'function funcName(a,n){}var globalVar;'
|
856 |
|
857 | UglifyJS.minify(code, { mangle: { reserved: ['firstLongName'] } }).code;
|
858 | // 'function funcName(firstLongName,a){}var globalVar;'
|
859 |
|
860 | UglifyJS.minify(code, { mangle: { toplevel: true } }).code;
|
861 | // 'function n(n,a){}var a;'
|
862 | ```
|
863 |
|
864 | ### Mangle properties options
|
865 |
|
866 | - `builtins` (default: `false`) — Use `true` to allow the mangling of builtin
|
867 | DOM properties. Not recommended to override this setting.
|
868 |
|
869 | - `debug` (default: `false`) — Mangle names with the original name still present.
|
870 | Pass an empty string `""` to enable, or a non-empty string to set the debug suffix.
|
871 |
|
872 | - `keep_quoted` (default: `false`) — Only mangle unquoted property names.
|
873 |
|
874 | - `regex` (default: `null`) — Pass a RegExp literal to only mangle property
|
875 | names matching the regular expression.
|
876 |
|
877 | - `reserved` (default: `[]`) — Do not mangle property names listed in the
|
878 | `reserved` array.
|
879 |
|
880 | ## Output options
|
881 |
|
882 | The code generator tries to output shortest code possible by default. In
|
883 | case you want beautified output, pass `--beautify` (`-b`). Optionally you
|
884 | can pass additional arguments that control the code output:
|
885 |
|
886 | - `annotations` (default: `false`) — pass `true` to retain comment annotations
|
887 | `/*@__PURE__*/` or `/*#__PURE__*/`, otherwise they will be discarded even if
|
888 | `comments` is set.
|
889 |
|
890 | - `ascii_only` (default: `false`) — escape Unicode characters in strings and
|
891 | regexps (affects directives with non-ascii characters becoming invalid)
|
892 |
|
893 | - `beautify` (default: `true`) — whether to actually beautify the output.
|
894 | Passing `-b` will set this to true, but you might need to pass `-b` even
|
895 | when you want to generate minified code, in order to specify additional
|
896 | arguments, so you can use `-b beautify=false` to override it.
|
897 |
|
898 | - `braces` (default: `false`) — always insert braces in `if`, `for`,
|
899 | `do`, `while` or `with` statements, even if their body is a single
|
900 | statement.
|
901 |
|
902 | - `comments` (default: `false`) — pass `true` or `"all"` to preserve all
|
903 | comments, `"some"` to preserve multi-line comments that contain `@cc_on`,
|
904 | `@license`, or `@preserve` (case-insensitive), a regular expression string
|
905 | (e.g. `/^!/`), or a function which returns `boolean`, e.g.
|
906 | ```javascript
|
907 | function(node, comment) {
|
908 | return comment.value.indexOf("@type " + node.TYPE) >= 0;
|
909 | }
|
910 | ```
|
911 |
|
912 | - `galio` (default: `false`) — enable workarounds for ANT Galio bugs
|
913 |
|
914 | - `indent_level` (default: `4`)
|
915 |
|
916 | - `indent_start` (default: `0`) — prefix all lines by that many spaces
|
917 |
|
918 | - `inline_script` (default: `true`) — escape HTML comments and the slash in
|
919 | occurrences of `</script>` in strings
|
920 |
|
921 | - `keep_quoted_props` (default: `false`) — when turned on, prevents stripping
|
922 | quotes from property names in object literals.
|
923 |
|
924 | - `max_line_len` (default: `false`) — maximum line length (for uglified code)
|
925 |
|
926 | - `preamble` (default: `null`) — when passed it must be a string and
|
927 | it will be prepended to the output literally. The source map will
|
928 | adjust for this text. Can be used to insert a comment containing
|
929 | licensing information, for example.
|
930 |
|
931 | - `preserve_line` (default: `false`) — pass `true` to retain line numbering on
|
932 | a best effort basis.
|
933 |
|
934 | - `quote_keys` (default: `false`) — pass `true` to quote all keys in literal
|
935 | objects
|
936 |
|
937 | - `quote_style` (default: `0`) — preferred quote style for strings (affects
|
938 | quoted property names and directives as well):
|
939 | - `0` — prefers double quotes, switches to single quotes when there are
|
940 | more double quotes in the string itself. `0` is best for gzip size.
|
941 | - `1` — always use single quotes
|
942 | - `2` — always use double quotes
|
943 | - `3` — always use the original quotes
|
944 |
|
945 | - `semicolons` (default: `true`) — separate statements with semicolons. If
|
946 | you pass `false` then whenever possible we will use a newline instead of a
|
947 | semicolon, leading to more readable output of uglified code (size before
|
948 | gzip could be smaller; size after gzip insignificantly larger).
|
949 |
|
950 | - `shebang` (default: `true`) — preserve shebang `#!` in preamble (bash scripts)
|
951 |
|
952 | - `width` (default: `80`) — only takes effect when beautification is on, this
|
953 | specifies an (orientative) line width that the beautifier will try to
|
954 | obey. It refers to the width of the line text (excluding indentation).
|
955 | It doesn't work very well currently, but it does make the code generated
|
956 | by UglifyJS more readable.
|
957 |
|
958 | - `wrap_iife` (default: `false`) — pass `true` to wrap immediately invoked
|
959 | function expressions. See
|
960 | [#640](https://github.com/mishoo/UglifyJS/issues/640) for more details.
|
961 |
|
962 | # Miscellaneous
|
963 |
|
964 | ### Keeping copyright notices or other comments
|
965 |
|
966 | You can pass `--comments` to retain certain comments in the output. By
|
967 | default it will keep JSDoc-style comments that contain "@preserve",
|
968 | "@license" or "@cc_on" (conditional compilation for IE). You can pass
|
969 | `--comments all` to keep all the comments, or a valid JavaScript regexp to
|
970 | keep only comments that match this regexp. For example `--comments /^!/`
|
971 | will keep comments like `/*! Copyright Notice */`.
|
972 |
|
973 | Note, however, that there might be situations where comments are lost. For
|
974 | example:
|
975 | ```javascript
|
976 | function f() {
|
977 | /** @preserve Foo Bar */
|
978 | function g() {
|
979 | // this function is never called
|
980 | }
|
981 | return something();
|
982 | }
|
983 | ```
|
984 |
|
985 | Even though it has "@preserve", the comment will be lost because the inner
|
986 | function `g` (which is the AST node to which the comment is attached to) is
|
987 | discarded by the compressor as not referenced.
|
988 |
|
989 | The safest comments where to place copyright information (or other info that
|
990 | needs to be kept in the output) are comments attached to toplevel nodes.
|
991 |
|
992 | ### The `unsafe` `compress` option
|
993 |
|
994 | It enables some transformations that *might* break code logic in certain
|
995 | contrived cases, but should be fine for most code. You might want to try it
|
996 | on your own code, it should reduce the minified size. Here's what happens
|
997 | when this flag is on:
|
998 |
|
999 | - `new Array(1, 2, 3)` or `Array(1, 2, 3)` → `[ 1, 2, 3 ]`
|
1000 | - `new Object()` → `{}`
|
1001 | - `String(exp)` or `exp.toString()` → `"" + exp`
|
1002 | - `new Object/RegExp/Function/Error/Array (...)` → we discard the `new`
|
1003 |
|
1004 | ### Conditional compilation
|
1005 |
|
1006 | You can use the `--define` (`-d`) switch in order to declare global
|
1007 | variables that UglifyJS will assume to be constants (unless defined in
|
1008 | scope). For example if you pass `--define DEBUG=false` then, coupled with
|
1009 | dead code removal UglifyJS will discard the following from the output:
|
1010 | ```javascript
|
1011 | if (DEBUG) {
|
1012 | console.log("debug stuff");
|
1013 | }
|
1014 | ```
|
1015 |
|
1016 | You can specify nested constants in the form of `--define env.DEBUG=false`.
|
1017 |
|
1018 | UglifyJS will warn about the condition being always false and about dropping
|
1019 | unreachable code; for now there is no option to turn off only this specific
|
1020 | warning, you can pass `warnings=false` to turn off *all* warnings.
|
1021 |
|
1022 | Another way of doing that is to declare your globals as constants in a
|
1023 | separate file and include it into the build. For example you can have a
|
1024 | `build/defines.js` file with the following:
|
1025 | ```javascript
|
1026 | var DEBUG = false;
|
1027 | var PRODUCTION = true;
|
1028 | // etc.
|
1029 | ```
|
1030 |
|
1031 | and build your code like this:
|
1032 |
|
1033 | uglifyjs build/defines.js js/foo.js js/bar.js... -c
|
1034 |
|
1035 | UglifyJS will notice the constants and, since they cannot be altered, it
|
1036 | will evaluate references to them to the value itself and drop unreachable
|
1037 | code as usual. The build will contain the `const` declarations if you use
|
1038 | them. If you are targeting < ES6 environments which does not support `const`,
|
1039 | using `var` with `reduce_vars` (enabled by default) should suffice.
|
1040 |
|
1041 | ### Conditional compilation API
|
1042 |
|
1043 | You can also use conditional compilation via the programmatic API. With the difference that the
|
1044 | property name is `global_defs` and is a compressor property:
|
1045 |
|
1046 | ```javascript
|
1047 | var result = UglifyJS.minify(fs.readFileSync("input.js", "utf8"), {
|
1048 | compress: {
|
1049 | dead_code: true,
|
1050 | global_defs: {
|
1051 | DEBUG: false
|
1052 | }
|
1053 | }
|
1054 | });
|
1055 | ```
|
1056 |
|
1057 | To replace an identifier with an arbitrary non-constant expression it is
|
1058 | necessary to prefix the `global_defs` key with `"@"` to instruct UglifyJS
|
1059 | to parse the value as an expression:
|
1060 | ```javascript
|
1061 | UglifyJS.minify("alert('hello');", {
|
1062 | compress: {
|
1063 | global_defs: {
|
1064 | "@alert": "console.log"
|
1065 | }
|
1066 | }
|
1067 | }).code;
|
1068 | // returns: 'console.log("hello");'
|
1069 | ```
|
1070 |
|
1071 | Otherwise it would be replaced as string literal:
|
1072 | ```javascript
|
1073 | UglifyJS.minify("alert('hello');", {
|
1074 | compress: {
|
1075 | global_defs: {
|
1076 | "alert": "console.log"
|
1077 | }
|
1078 | }
|
1079 | }).code;
|
1080 | // returns: '"console.log"("hello");'
|
1081 | ```
|
1082 |
|
1083 | ### Using native Uglify AST with `minify()`
|
1084 | ```javascript
|
1085 | // example: parse only, produce native Uglify AST
|
1086 |
|
1087 | var result = UglifyJS.minify(code, {
|
1088 | parse: {},
|
1089 | compress: false,
|
1090 | mangle: false,
|
1091 | output: {
|
1092 | ast: true,
|
1093 | code: false // optional - faster if false
|
1094 | }
|
1095 | });
|
1096 |
|
1097 | // result.ast contains native Uglify AST
|
1098 | ```
|
1099 | ```javascript
|
1100 | // example: accept native Uglify AST input and then compress and mangle
|
1101 | // to produce both code and native AST.
|
1102 |
|
1103 | var result = UglifyJS.minify(ast, {
|
1104 | compress: {},
|
1105 | mangle: {},
|
1106 | output: {
|
1107 | ast: true,
|
1108 | code: true // optional - faster if false
|
1109 | }
|
1110 | });
|
1111 |
|
1112 | // result.ast contains native Uglify AST
|
1113 | // result.code contains the minified code in string form.
|
1114 | ```
|
1115 |
|
1116 | ### Working with Uglify AST
|
1117 |
|
1118 | Transversal and transformation of the native AST can be performed through
|
1119 | [`TreeWalker`](https://github.com/mishoo/UglifyJS/blob/master/lib/ast.js) and
|
1120 | [`TreeTransformer`](https://github.com/mishoo/UglifyJS/blob/master/lib/transform.js)
|
1121 | respectively.
|
1122 |
|
1123 | ### ESTree / SpiderMonkey AST
|
1124 |
|
1125 | UglifyJS has its own abstract syntax tree format; for
|
1126 | [practical reasons](http://lisperator.net/blog/uglifyjs-why-not-switching-to-spidermonkey-ast/)
|
1127 | we can't easily change to using the SpiderMonkey AST internally. However,
|
1128 | UglifyJS now has a converter which can import a SpiderMonkey AST.
|
1129 |
|
1130 | For example [Acorn][acorn] is a super-fast parser that produces a
|
1131 | SpiderMonkey AST. It has a small CLI utility that parses one file and dumps
|
1132 | the AST in JSON on the standard output. To use UglifyJS to mangle and
|
1133 | compress that:
|
1134 |
|
1135 | acorn file.js | uglifyjs -p spidermonkey -m -c
|
1136 |
|
1137 | The `-p spidermonkey` option tells UglifyJS that all input files are not
|
1138 | JavaScript, but JS code described in SpiderMonkey AST in JSON. Therefore we
|
1139 | don't use our own parser in this case, but just transform that AST into our
|
1140 | internal AST.
|
1141 |
|
1142 | ### Use Acorn for parsing
|
1143 |
|
1144 | More for fun, I added the `-p acorn` option which will use Acorn to do all
|
1145 | the parsing. If you pass this option, UglifyJS will `require("acorn")`.
|
1146 |
|
1147 | Acorn is really fast (e.g. 250ms instead of 380ms on some 650K code), but
|
1148 | converting the SpiderMonkey tree that Acorn produces takes another 150ms so
|
1149 | in total it's a bit more than just using UglifyJS's own parser.
|
1150 |
|
1151 | [acorn]: https://github.com/ternjs/acorn
|
1152 | [sm-spec]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k
|
1153 |
|
1154 | ### Uglify Fast Minify Mode
|
1155 |
|
1156 | It's not well known, but whitespace removal and symbol mangling accounts
|
1157 | for 95% of the size reduction in minified code for most JavaScript - not
|
1158 | elaborate code transforms. One can simply disable `compress` to speed up
|
1159 | Uglify builds by 3 to 5 times.
|
1160 |
|
1161 | | d3.js | minify size | gzip size | minify time (seconds) |
|
1162 | | --- | ---: | ---: | ---: |
|
1163 | | original | 511,371 | 119,932 | - |
|
1164 | | uglify-js@3.13.0 mangle=false, compress=false | 363,988 | 95,695 | 0.56 |
|
1165 | | uglify-js@3.13.0 mangle=true, compress=false | 253,305 | 81,281 | 0.99 |
|
1166 | | uglify-js@3.13.0 mangle=true, compress=true | 244,436 | 79,854 | 5.30 |
|
1167 |
|
1168 | To enable fast minify mode from the CLI use:
|
1169 | ```
|
1170 | uglifyjs file.js -m
|
1171 | ```
|
1172 | To enable fast minify mode with the API use:
|
1173 | ```javascript
|
1174 | UglifyJS.minify(code, { compress: false, mangle: true });
|
1175 | ```
|
1176 |
|
1177 | ### Source maps and debugging
|
1178 |
|
1179 | Various `compress` transforms that simplify, rearrange, inline and remove code
|
1180 | are known to have an adverse effect on debugging with source maps. This is
|
1181 | expected as code is optimized and mappings are often simply not possible as
|
1182 | some code no longer exists. For highest fidelity in source map debugging
|
1183 | disable the Uglify `compress` option and just use `mangle`.
|
1184 |
|
1185 | ### Compiler assumptions
|
1186 |
|
1187 | To allow for better optimizations, the compiler makes various assumptions:
|
1188 |
|
1189 | - The code does not rely on preserving its runtime performance characteristics.
|
1190 | Typically uglified code will run faster due to less instructions and easier
|
1191 | inlining, but may be slower on rare occasions for a specific platform, e.g.
|
1192 | see [`reduce_funcs`](#compress-options).
|
1193 | - `.toString()` and `.valueOf()` don't have side effects, and for built-in
|
1194 | objects they have not been overridden.
|
1195 | - `undefined`, `NaN` and `Infinity` have not been externally redefined.
|
1196 | - `arguments.callee`, `arguments.caller` and `Function.prototype.caller` are not used.
|
1197 | - The code doesn't expect the contents of `Function.prototype.toString()` or
|
1198 | `Error.prototype.stack` to be anything in particular.
|
1199 | - Getting and setting properties on a plain object does not cause other side effects
|
1200 | (using `.watch()` or `Proxy`).
|
1201 | - Object properties can be added, removed and modified (not prevented with
|
1202 | `Object.defineProperty()`, `Object.defineProperties()`, `Object.freeze()`,
|
1203 | `Object.preventExtensions()` or `Object.seal()`).
|
1204 | - Earlier versions of JavaScript will throw `SyntaxError` with the following:
|
1205 | ```javascript
|
1206 | ({
|
1207 | p: 42,
|
1208 | get p() {},
|
1209 | });
|
1210 | // SyntaxError: Object literal may not have data and accessor property with
|
1211 | // the same name
|
1212 | ```
|
1213 | UglifyJS may modify the input which in turn may suppress those errors.
|
1214 | - Iteration order of keys over an object which contains spread syntax in later
|
1215 | versions of Chrome and Node.js may be altered.
|
1216 | - When `toplevel` is enabled, UglifyJS effectively assumes input code is wrapped
|
1217 | within `function(){ ... }`, thus forbids aliasing of declared global variables:
|
1218 | ```javascript
|
1219 | A = "FAIL";
|
1220 | var B = "FAIL";
|
1221 | // can be `global`, `self`, `window` etc.
|
1222 | var top = function() {
|
1223 | return this;
|
1224 | }();
|
1225 | // "PASS"
|
1226 | top.A = "PASS";
|
1227 | console.log(A);
|
1228 | // "FAIL" after compress and/or mangle
|
1229 | top.B = "PASS";
|
1230 | console.log(B);
|
1231 | ```
|
1232 | - Use of `arguments` alongside destructuring as function parameters, e.g.
|
1233 | `function({}, arguments) {}` will result in `SyntaxError` in earlier versions
|
1234 | of Chrome and Node.js - UglifyJS may modify the input which in turn may
|
1235 | suppress those errors.
|
1236 | - Earlier versions of Chrome and Node.js will throw `ReferenceError` with the
|
1237 | following:
|
1238 | ```javascript
|
1239 | var a;
|
1240 | try {
|
1241 | throw 42;
|
1242 | } catch ({
|
1243 | [a]: b,
|
1244 | // ReferenceError: a is not defined
|
1245 | }) {
|
1246 | let a;
|
1247 | }
|
1248 | ```
|
1249 | UglifyJS may modify the input which in turn may suppress those errors.
|
1250 | - Later versions of JavaScript will throw `SyntaxError` with the following:
|
1251 | ```javascript
|
1252 | a => {
|
1253 | let a;
|
1254 | };
|
1255 | // SyntaxError: Identifier 'a' has already been declared
|
1256 | ```
|
1257 | UglifyJS may modify the input which in turn may suppress those errors.
|
1258 | - Later versions of JavaScript will throw `SyntaxError` with the following:
|
1259 | ```javascript
|
1260 | try {
|
1261 | // ...
|
1262 | } catch ({ message: a }) {
|
1263 | var a;
|
1264 | }
|
1265 | // SyntaxError: Identifier 'a' has already been declared
|
1266 | ```
|
1267 | UglifyJS may modify the input which in turn may suppress those errors.
|
1268 | - Some versions of Chrome and Node.js will throw `ReferenceError` with the
|
1269 | following:
|
1270 | ```javascript
|
1271 | console.log(((a, b = function() {
|
1272 | return a;
|
1273 | // ReferenceError: a is not defined
|
1274 | }()) => b)());
|
1275 | ```
|
1276 | UglifyJS may modify the input which in turn may suppress those errors.
|
1277 | - Some arithmetic operations with `BigInt` may throw `TypeError`:
|
1278 | ```javascript
|
1279 | 1n + 1;
|
1280 | // TypeError: can't convert BigInt to number
|
1281 | ```
|
1282 | UglifyJS may modify the input which in turn may suppress those errors.
|
1283 | - Some versions of JavaScript will throw `SyntaxError` with the
|
1284 | following:
|
1285 | ```javascript
|
1286 | console.log(String.raw`\uFo`);
|
1287 | // SyntaxError: Invalid Unicode escape sequence
|
1288 | ```
|
1289 | UglifyJS may modify the input which in turn may suppress those errors.
|
1290 | - Some versions of JavaScript will throw `SyntaxError` with the
|
1291 | following:
|
1292 | ```javascript
|
1293 | try {} catch (e) {
|
1294 | for (var e of []);
|
1295 | }
|
1296 | // SyntaxError: Identifier 'e' has already been declared
|
1297 | ```
|
1298 | UglifyJS may modify the input which in turn may suppress those errors.
|
1299 | - Some versions of Chrome and Node.js will give incorrect results with the
|
1300 | following:
|
1301 | ```javascript
|
1302 | console.log({
|
1303 | ...{
|
1304 | set 42(v) {},
|
1305 | 42: "PASS",
|
1306 | },
|
1307 | });
|
1308 | // Expected: { '42': 'PASS' }
|
1309 | // Actual: { '42': undefined }
|
1310 | ```
|
1311 | UglifyJS may modify the input which in turn may suppress those errors.
|
1312 |
|
\ | No newline at end of file |