clean-css is a fast and efficient CSS optimizer for Node.js platform and any modern browser.
According to tests it is one of the best available.
Table of Contents
@imports correctly?clean-css requires Node.js 4.0+ (tested on Linux, OS X, and Windows)
npm install --save-dev clean-css
js
var CleanCSS = require('clean-css');
var input = 'a{font-weight:bold;}';
var options = { /* options */ };
var output = new CleanCSS(options).minify(input);
clean-css 4.0 introduces some breaking changes:
root, relativeTo, and target options are replaced by a single rebaseTo option - this means that rebasing URLs and import inlining is much simpler but may not be (YMMV) as powerful as in 3.x;debug option is gone as stats are always provided in output object under stats property;roundingPrecision is disabled by default;roundingPrecision applies to all units now, not only px as in 3.x;processImport and processImportFrom are merged into inline option which defaults to local. Remote @import rules are NOT inlined by default anymore;inliner: { request: ..., timeout: ... } option into inlineRequest and inlineTimeout options;//fonts.googleapis.com/css?family=Domine:700, are not inlined anymore;{ compatibility: 'ie9' } flag;keepSpecialComments to specialComments;roundingPrecision and specialComments to level 1 optimizations options, see examples;mediaMerging, restructuring, semanticMerging, and shorthandCompacting to level 2 optimizations options, see examples below;shorthandCompacting option to mergeIntoShorthands;keepBreaks option is replaced with { format: 'keep-breaks' } to ease transition;sourceMap option has to be a boolean from now on - to specify an input source map pass it a 2nd argument to minify method or via a hash instead;aggressiveMerging option is removed as aggressive merging is replaced by smarter override merging.clean-css 4.1 introduces the following changes / features:
inline: false as an alias to inline: ['none'];multiplePseudoMerging compatibility flag controlling merging of rules with multiple pseudo classes / elements;removeEmpty flag in level 1 optimizations controlling removal of rules and nested blocks;removeEmpty flag in level 2 optimizations controlling removal of rules and nested blocks;compatibility: { selectors: { mergeLimit: <number> } } flag in compatibility settings controlling maximum number of selectors in a single rule;minify method improved signature accepting a list of hashes for a predictable traversal;selectorsSortingMethod level 1 optimization allows false or 'none' for disabling selector sorting;fetch option controlling a function for handling remote requests;font shorthand and font-* longhand optimizers;optimizeFont flag in level 1 optimizations due to new font shorthand optimizer;skipProperties flag in level 2 optimizations controlling which properties won't be optimized;animation shorthand and animation-* longhand optimizers;removeUnusedAtRules level 2 optimization controlling removal of unused @counter-style, @font-face, @keyframes, and @namespace at rules;clean-css 4.2 introduces the following changes / features:
process method for compatibility with optimize-css-assets-webpack-plugin;transition property optimizer;/* clean-css ignore:start */ and /* clean-css ignore:end */ comments;transform callback, see example;format: { breakWith: 'lf' } option.clean-css constructor accepts a hash as a parameter with the following options available:
compatibility - controls compatibility mode used; defaults to ie10+; see compatibility modes for examples;fetch - controls a function for handling remote requests; see fetch option for examples (since 4.1.0);format - controls output CSS formatting; defaults to false; see formatting options for examples;inline - controls @import inlining rules; defaults to 'local'; see inlining options for examples;inlineRequest - controls extra options for inlining remote @import rules, can be any of HTTP(S) request options;inlineTimeout - controls number of milliseconds after which inlining a remote @import fails; defaults to 5000;level - controls optimization level used; defaults to 1; see optimization levels for examples;rebase - controls URL rebasing; defaults to true;rebaseTo - controls a directory to which all URLs are rebased, most likely the directory under which the output file will live; defaults to the current directory;returnPromise - controls whether minify method returns a Promise object or not; defaults to false; see promise interface for examples;sourceMap - controls whether an output source map is built; defaults to false;sourceMapInlineSources - controls embedding sources inside a source map's sourcesContent field; defaults to false.There is a certain number of compatibility mode shortcuts, namely:
new CleanCSS({ compatibility: '*' }) (default) - Internet Explorer 10+ compatibility modenew CleanCSS({ compatibility: 'ie9' }) - Internet Explorer 9+ compatibility modenew CleanCSS({ compatibility: 'ie8' }) - Internet Explorer 8+ compatibility modenew CleanCSS({ compatibility: 'ie7' }) - Internet Explorer 7+ compatibility modeEach of these modes is an alias to a fine grained configuration, with the following options available:
js
new CleanCSS({
compatibility: {
colors: {
opacity: true // controls `rgba()` / `hsla()` color support
},
properties: {
backgroundClipMerging: true, // controls background-clip merging into shorthand
backgroundOriginMerging: true, // controls background-origin merging into shorthand
backgroundSizeMerging: true, // controls background-size merging into shorthand
colors: true, // controls color optimizations
ieBangHack: false, // controls keeping IE bang hack
ieFilters: false, // controls keeping IE `filter` / `-ms-filter`
iePrefixHack: false, // controls keeping IE prefix hack
ieSuffixHack: false, // controls keeping IE suffix hack
merging: true, // controls property merging based on understandability
shorterLengthUnits: false, // controls shortening pixel units into `pc`, `pt`, or `in` units
spaceAfterClosingBrace: true, // controls keeping space after closing brace - `url() no-repeat` into `url()no-repeat`
urlQuotes: false, // controls keeping quoting inside `url()`
zeroUnits: true // controls removal of units `0` value
},
selectors: {
adjacentSpace: false, // controls extra space before `nav` element
ie7Hack: true, // controls removal of IE7 selector hacks, e.g. `*+html...`
mergeablePseudoClasses: [':active', ...], // controls a whitelist of mergeable pseudo classes
mergeablePseudoElements: ['::after', ...], // controls a whitelist of mergeable pseudo elements
mergeLimit: 8191, // controls maximum number of selectors in a single rule (since 4.1.0)
multiplePseudoMerging: true // controls merging of rules with multiple pseudo classes / elements (since 4.1.0)
},
units: {
ch: true, // controls treating `ch` as a supported unit
in: true, // controls treating `in` as a supported unit
pc: true, // controls treating `pc` as a supported unit
pt: true, // controls treating `pt` as a supported unit
rem: true, // controls treating `rem` as a supported unit
vh: true, // controls treating `vh` as a supported unit
vm: true, // controls treating `vm` as a supported unit
vmax: true, // controls treating `vmax` as a supported unit
vmin: true // controls treating `vmin` as a supported unit
}
}
})
You can also use a string when setting a compatibility mode, e.g.
js
new CleanCSS({
compatibility: 'ie9,-properties.merging' // sets compatibility to IE9 mode with disabled property merging
})
The fetch option accepts a function which handles remote resource fetching, e.g.
js
var request = require('request');
var source = '@import url(http://example.com/path/to/stylesheet.css);';
new CleanCSS({
fetch: function (uri, inlineRequest, inlineTimeout, callback) {
request(uri, function (error, response, body) {
if (error) {
callback(error, null);
} else if (response && response.statusCode != 200) {
callback(response.statusCode, null);
} else {
callback(null, body);
}
});
}
}).minify(source);
This option provides a convenient way of overriding the default fetching logic if it doesn't support a particular feature, say CONNECT proxies.
Unless given, the default loadRemoteResource logic is used.
By default output CSS is formatted without any whitespace unless a format option is given.
First of all there are two shorthands:
js
new CleanCSS({
format: 'beautify' // formats output in a really nice way
})
and
js
new CleanCSS({
format: 'keep-breaks' // formats output the default way but adds line breaks for improved readability
})
however format option also accept a fine-grained set of options:
js
new CleanCSS({
format: {
breaks: { // controls where to insert breaks
afterAtRule: false, // controls if a line break comes after an at-rule; e.g. `@charset`; defaults to `false`
afterBlockBegins: false, // controls if a line break comes after a block begins; e.g. `@media`; defaults to `false`
afterBlockEnds: false, // controls if a line break comes after a block ends, defaults to `false`
afterComment: false, // controls if a line break comes after a comment; defaults to `false`
afterProperty: false, // controls if a line break comes after a property; defaults to `false`
afterRuleBegins: false, // controls if a line break comes after a rule begins; defaults to `false`
afterRuleEnds: false, // controls if a line break comes after a rule ends; defaults to `false`
beforeBlockEnds: false, // controls if a line break comes before a block ends; defaults to `false`
betweenSelectors: false // controls if a line break comes between selectors; defaults to `false`
},
breakWith: '\n', // controls the new line character, can be `'\r\n'` or `'\n'` (aliased as `'windows'` and `'unix'` or `'crlf'` and `'lf'`); defaults to system one, so former on Windows and latter on Unix
indentBy: 0, // controls number of characters to indent with; defaults to `0`
indentWith: 'space', // controls a character to indent with, can be `'space'` or `'tab'`; defaults to `'space'`
spaces: { // controls where to insert spaces
aroundSelectorRelation: false, // controls if spaces come around selector relations; e.g. `div > a`; defaults to `false`
beforeBlockBegins: false, // controls if a space comes before a block begins; e.g. `.block {`; defaults to `false`
beforeValue: false // controls if a space comes before a value; e.g. `width: 1rem`; defaults to `false`
},
wrapAt: false // controls maximum line length; defaults to `false`
}
})
inline option whitelists which @import rules will be processed, e.g.
js
new CleanCSS({
inline: ['local'] // default; enables local inlining only
})
js
new CleanCSS({
inline: ['none'] // disables all inlining
})
```js // introduced in clean-css 4.1.0
new CleanCSS({
inline: false // disables all inlining (alias to ['none'])
})
```
js
new CleanCSS({
inline: ['all'] // enables all inlining, same as ['local', 'remote']
})
js
new CleanCSS({
inline: ['local', 'mydomain.example.com'] // enables local inlining plus given remote source
})
js
new CleanCSS({
inline: ['local', 'remote', '!fonts.googleapis.com'] // enables all inlining but from given remote source
})
The level option can be either 0, 1 (default), or 2, e.g.
js
new CleanCSS({
level: 2
})
or a fine-grained configuration given via a hash.
Please note that level 1 optimization options are generally safe while level 2 optimizations should be safe for most users.
Level 0 optimizations simply means "no optimizations". Use it when you'd like to inline imports and / or rebase URLs but skip everything else.
Level 1 optimizations (default) operate on single properties only, e.g. can remove units when not required, turn rgb colors to a shorter hex representation, remove comments, etc
Here is a full list of available options:
js
new CleanCSS({
level: {
1: {
cleanupCharsets: true, // controls `@charset` moving to the front of a stylesheet; defaults to `true`
normalizeUrls: true, // controls URL normalization; defaults to `true`
optimizeBackground: true, // controls `background` property optimizations; defaults to `true`
optimizeBorderRadius: true, // controls `border-radius` property optimizations; defaults to `true`
optimizeFilter: true, // controls `filter` property optimizations; defaults to `true`
optimizeFont: true, // controls `font` property optimizations; defaults to `true`
optimizeFontWeight: true, // controls `font-weight` property optimizations; defaults to `true`
optimizeOutline: true, // controls `outline` property optimizations; defaults to `true`
removeEmpty: true, // controls removing empty rules and nested blocks; defaults to `true`
removeNegativePaddings: true, // controls removing negative paddings; defaults to `true`
removeQuotes: true, // controls removing quotes when unnecessary; defaults to `true`
removeWhitespace: true, // controls removing unused whitespace; defaults to `true`
replaceMultipleZeros: true, // contols removing redundant zeros; defaults to `true`
replaceTimeUnits: true, // controls replacing time units with shorter values; defaults to `true`
replaceZeroUnits: true, // controls replacing zero values with units; defaults to `true`
roundingPrecision: false, // rounds pixel values to `N` decimal places; `false` disables rounding; defaults to `false`
selectorsSortingMethod: 'standard', // denotes selector sorting method; can be `'natural'` or `'standard'`, `'none'`, or false (the last two since 4.1.0); defaults to `'standard'`
specialComments: 'all', // denotes a number of /*! ... */ comments preserved; defaults to `all`
tidyAtRules: true, // controls at-rules (e.g. `@charset`, `@import`) optimizing; defaults to `true`
tidyBlockScopes: true, // controls block scopes (e.g. `@media`) optimizing; defaults to `true`
tidySelectors: true, // controls selectors optimizing; defaults to `true`,
semicolonAfterLastProperty: false, // controls removing trailing semicolons in rule; defaults to `false` - means remove
transform: function () {} // defines a callback for fine-grained property optimization; defaults to no-op
}
}
});
There is an all shortcut for toggling all options at the same time, e.g.
js
new CleanCSS({
level: {
1: {
all: false, // set all values to `false`
tidySelectors: true // turns on optimizing selectors
}
}
});
Level 2 optimizations operate at rules or multiple properties level, e.g. can remove duplicate rules, remove properties redefined further down a stylesheet, or restructure rules by moving them around.
Please note that if level 2 optimizations are turned on then, unless explicitely disabled, level 1 optimizations are applied as well.
Here is a full list of available options:
js
new CleanCSS({
level: {
2: {
mergeAdjacentRules: true, // controls adjacent rules merging; defaults to true
mergeIntoShorthands: true, // controls merging properties into shorthands; defaults to true
mergeMedia: true, // controls `@media` merging; defaults to true
mergeNonAdjacentRules: true, // controls non-adjacent rule merging; defaults to true
mergeSemantically: false, // controls semantic merging; defaults to false
overrideProperties: true, // controls property overriding based on understandability; defaults to true
removeEmpty: true, // controls removing empty rules and nested blocks; defaults to `true`
reduceNonAdjacentRules: true, // controls non-adjacent rule reducing; defaults to true
removeDuplicateFontRules: true, // controls duplicate `@font-face` removing; defaults to true
removeDuplicateMediaBlocks: true, // controls duplicate `@media` removing; defaults to true
removeDuplicateRules: true, // controls duplicate rules removing; defaults to true
removeUnusedAtRules: false, // controls unused at rule removing; defaults to false (available since 4.1.0)
restructureRules: false, // controls rule restructuring; defaults to false
skipProperties: [] // controls which properties won't be optimized, defaults to `[]` which means all will be optimized (since 4.1.0)
}
}
});
There is an all shortcut for toggling all options at the same time, e.g.
js
new CleanCSS({
level: {
2: {
all: false, // sets all values to `false`
removeDuplicateRules: true // turns on removing duplicate rules
}
}
});
Once configured clean-css provides a minify method to optimize a given CSS, e.g.
js
var output = new CleanCSS(options).minify(source);
The output of the minify method is a hash with following fields:
js
console.log(output.styles); // optimized output CSS as a string
console.log(output.sourceMap); // output source map if requested with `sourceMap` option
console.log(output.errors); // a list of errors raised
console.log(output.warnings); // a list of warnings raised
console.log(output.stats.originalSize); // original content size after import inlining
console.log(output.stats.minifiedSize); // optimized content size
console.log(output.stats.timeSpent); // time spent on optimizations in milliseconds
console.log(output.stats.efficiency); // `(originalSize - minifiedSize) / originalSize`, e.g. 0.25 if size is reduced from 100 bytes to 75 bytes
The minify method also accepts an input source map, e.g.
js
var output = new CleanCSS(options).minify(source, inputSourceMap);
or a callback invoked when optimizations are finished, e.g.
js
new CleanCSS(options).minify(source, function (error, output) {
// `output` is the same as in the synchronous call above
});
If you prefer clean-css to return a Promise object then you need to explicitely ask for it, e.g.
js
new CleanCSS({ returnPromise: true })
.minify(source)
.then(function (output) { console.log(output.styles); })
.catch(function (error) { // deal with errors });
Clean-css has an associated command line utility that can be installed separately using npm install clean-css-cli. For more detailed information, please visit https://github.com/jakubpawlowicz/clean-css-cli.
It can be done either by passing an array of paths, or, when sources are already available, a hash or an array of hashes:
js
new CleanCSS().minify(['path/to/file/one', 'path/to/file/two']);
js
new CleanCSS().minify({
'path/to/file/one': {
styles: 'contents of file one'
},
'path/to/file/two': {
styles: 'contents of file two'
}
});
js
new CleanCSS().minify([
{'path/to/file/one': {styles: 'contents of file one'}},
{'path/to/file/two': {styles: 'contents of file two'}}
]);
Passing an array of hashes allows you to explicitly specify the order in which the input files are concatenated. Whereas when you use a single hash the order is determined by the traversal order of object properties - available since 4.1.0.
Important note - any @import rules already present in the hash will be resolved in memory.
@imports correctly?In order to inline remote @import statements you need to provide a callback to minify method as fetching remote assets is an asynchronous operation, e.g.:
js
var source = '@import url(http://example.com/path/to/remote/styles);';
new CleanCSS({ inline: ['remote'] }).minify(source, function (error, output) {
// output.styles
});
If you don't provide a callback, then remote @imports will be left as is.
If clean-css doesn't perform a particular property optimization, you can use transform callback to apply it:
``js
var source = '.block{background-image:url(/path/to/image.png)}';
var output = new CleanCSS({
level: {
1: {
transform: function (propertyName, propertyValue, selector /*selector` available since 4.2.0-pre */) {
if (propertyName == 'background-image' && propertyValue.indexOf('/path/to') > -1) {
return propertyValue.replace('/path/to', '../valid/path/to');
}
}
}
}
}).minify(source);
console.log(output.styles); # => .block{background-image:url(../valid/path/to/image.png)} ```
Note: returning false from transform callback will drop a property.
The level 1 roundingPrecision optimization option accept a string with per-unit rounding precision settings, e.g.
js
new CleanCSS({
level: {
1: {
roundingPrecision: 'all=3,px=5'
}
}
}).minify(source)
which sets all units rounding precision to 3 digits except px unit precision of 5 digits.
Note: available in the current master, to be released in 4.2.0.
Wrap the CSS fragment in special comments which instruct clean-css to preserve it, e.g.
css
.block-1 {
color: red
}
/* clean-css ignore:start */
.block-special {
color: transparent
}
/* clean-css ignore:end */
.block-2 {
margin: 0
}
Optimizing this CSS will result in the following output:
css
.block-1{color:red}
.block-special {
color: transparent
}
.block-2{margin:0}
Use the /*! notation instead of the standard one /*:
css
/*!
Important comments included in optimized output.
*/
clean-css will handle it automatically for you in the following cases:
rebaseTo is used with any of above two.To generate a source map, use sourceMap: true option, e.g.:
js
new CleanCSS({ sourceMap: true, rebaseTo: pathToOutputDirectory })
.minify(source, function (error, output) {
// access output.sourceMap for SourceMapGenerator object
// see https://github.com/mozilla/source-map/#sourcemapgenerator for more details
});
You can also pass an input source map directly as a 2nd argument to minify method:
js
new CleanCSS({ sourceMap: true, rebaseTo: pathToOutputDirectory })
.minify(source, inputSourceMap, function (error, output) {
// access output.sourceMap to access SourceMapGenerator object
// see https://github.com/mozilla/source-map/#sourcemapgenerator for more details
});
or even multiple input source maps at once:
js
new CleanCSS({ sourceMap: true, rebaseTo: pathToOutputDirectory }).minify({
'path/to/source/1': {
styles: '...styles...',
sourceMap: '...source-map...'
},
'path/to/source/2': {
styles: '...styles...',
sourceMap: '...source-map...'
}
}, function (error, output) {
// access output.sourceMap as above
});
Using the hash configuration specifying both optimization levels, e.g.
js
new CleanCSS({
level: {
1: {
all: true,
normalizeUrls: false
},
2: {
restructureRules: true
}
}
})
will apply level 1 optimizations, except url normalization, and default level 2 optimizations with rule restructuring.
All level 2 optimizations are dispatched here, and this is what they do:
recursivelyOptimizeBlocks - does all the following operations on a nested block, like @media or @keyframe;recursivelyOptimizeProperties - optimizes properties in rulesets and flat at-rules, like @font-face, by splitting them into components (e.g. margin into margin-(bottom|left|right|top)), optimizing, and restoring them back. You may want to use mergeIntoShorthands option to control whether you want to turn multiple components into shorthands;removeDuplicates - gets rid of duplicate rulesets with exactly the same set of properties, e.g. when including a Sass / Less partial twice for no good reason;mergeAdjacent - merges adjacent rulesets with the same selector or rules;reduceNonAdjacent - identifies which properties are overridden in same-selector non-adjacent rulesets, and removes them;mergeNonAdjacentBySelector - identifies same-selector non-adjacent rulesets which can be moved (!) to be merged, requires all intermediate rulesets to not redefine the moved properties, or if redefined to have the same value;mergeNonAdjacentByBody - same as the one above but for same-selector non-adjacent rulesets;restructure - tries to reorganize different-selector different-rules rulesets so they take less space, e.g. .one{padding:0}.two{margin:0}.one{margin-bottom:3px} into .two{margin:0}.one{padding:0;margin-bottom:3px};removeDuplicateFontAtRules - removes duplicated @font-face rules;removeDuplicateMediaQueries - removes duplicated @media nested blocks;mergeMediaQueries - merges non-adjacent @media at-rules by the same rules as mergeNonAdjacentBy* above;There is a number of 3rd party plugins to popular build tools:
See CONTRIBUTING.md.
First clone the sources:
bash
git clone git@github.com:jakubpawlowicz/clean-css.git
then install dependencies:
bash
cd clean-css
npm install
then use any of the following commands to verify your copy:
bash
npm run bench # for clean-css benchmarks (see [test/bench.js](https://github.com/jakubpawlowicz/clean-css/blob/master/test/bench.js) for details)
npm run browserify # to create the browser-ready clean-css version
npm run check # to lint JS sources with [JSHint](https://github.com/jshint/jshint/)
npm test # to run all tests
Sorted alphabetically by GitHub handle:
@import processing;@import processing inside comments;minify method source traversal in ES6;sys package;@import inlining and URL rebasing.@import inlining behavior;clean-css is released under the MIT License.