CSSO (CSS Optimizer) is a CSS minifier. It performs three sort of transformations: cleaning (removing redundant), compression (replacement for shorter form) and restructuring (merge of declarations, rulesets and so on). As a result your CSS becomes much smaller.

Usage

npm install -g csso

Runners

• Gulp: gulp-csso
• Grunt: grunt-csso
• Broccoli: broccoli-csso

Command line

csso [input] [output] [options]

Options:

      --debug [level]       Output intermediate state of CSS during compression
  -h, --help                Output usage information
  -i, --input <filename>    Input file
      --input-map <source>  Input source map. Possible values: none, auto (default) or <filename>
  -m, --map <destination>   Generate source map. Possible values: none (default), inline, file or <filename>
  -o, --output <filename>   Output file (result outputs to stdout if not set)
      --restructure-off     Turns structure minimization off
      --stat                Output statistics in stderr
  -v, --version             Output version

Some examples:

> csso in.css out.css

> csso in.css
...output result in stdout...

> echo '.test { color: #ff0000; }' | csso
.test{color:red}

> cat source1.css source2.css | csso | gzip -9 -c > production.css.gz

> echo '.test { color: #ff0000 }' | csso --stat >/dev/null
File:       <stdin>
Original:   25 bytes
Compressed: 16 bytes (64.00%)
Saving:     9 bytes (36.00%)
Time:       12 ms
Memory:     0.346 MB

Source maps

Source map doesn't generate by default. To generate map use --map CLI option, that can be:

• none (default) – don't generate source map
• inline – generate map add it into result content (via /*# sourceMappingURL=application/json;base64,...base64 encoded map... */)
• file – generate map and write it into file with same name as output file, but with .map extension; in this case --output option is required
• any other values treat as filename for generated source map

Examples:

> csso my.css --map inline
> csso my.css --map file --output my.min.css
> csso my.css -o my.min.css -m maps/my.min.map

Input can has a source map. Use --input-map option to specify input source map if needed. Possible values for option:

• auto (auto) - attempt to fetch input source map by follow steps:
  • try to fetch inline map from source
  • try to fetch map filename from source and read its content
  • (when --input is specified) check for file with same name as input but with .map extension exists and read its content
• none - don't use input source map; actually it's using to disable auto-fetching
• any other values treat as filename for input source map

NOTE: Input source map is using only if source map is generating.

API

var csso = require('csso');

var compressedCss = csso.minify('.test { color: #ff0000; }');

console.log(compressedCss);
// .test{color:red}


// there are some options you can pass
var compressedWithOptions = csso.minify('.test { color: #ff0000; }', {
    restructure: false,   // don't change css structure, i.e. don't merge declarations, rulesets etc
    debug: true           // show additional debug information:
                          // true or number from 1 to 3 (greater number - more details)
});

You may minify CSS by yourself step by step:

var ast = csso.parse('.test { color: #ff0000; }');
var compressedAst = csso.compress(ast);
var compressedCss = csso.translate(compressedAst, true);

console.log(compressedCss);
// .test{color:red}

Working with source maps:

var css = fs.readFileSync('path/to/my.css', 'utf8');
var result = csso.minify(css, {
  filename: 'path/to/my.css', // will be added to source map as reference to source file
  sourceMap: true             // generate source map
});

console.log(result);
// { css: '...minified...', map: SourceMapGenerator {} }

console.log(result.map.toString());
// '{ .. source map content .. }'

Debugging

> echo '.test { color: green; color: #ff0000 } .foo { color: red }' | csso --debug
## parsing done in 10 ms

Compress block #1
(0.002ms) convertToInternal
(0.000ms) clean
(0.001ms) compress
(0.002ms) prepare
(0.000ms) initialRejoinRuleset
(0.000ms) rejoinAtrule
(0.000ms) disjoin
(0.000ms) buildMaps
(0.000ms) markShorthands
(0.000ms) processShorthand
(0.001ms) restructBlock
(0.000ms) rejoinRuleset
(0.000ms) restructRuleset
## compressing done in 9 ms

.foo,.test{color:red}

More details are provided when --debug flag has a number greater than 1:

> echo '.test { color: green; color: #ff0000 } .foo { color: red }' | csso --debug 2
## parsing done in 8 ms

Compress block #1
(0.000ms) clean
  .test{color:green;color:#ff0000}.foo{color:red}

(0.001ms) compress
  .test{color:green;color:red}.foo{color:red}

...

(0.002ms) restructBlock
  .test{color:red}.foo{color:red}

(0.001ms) rejoinRuleset
  .foo,.test{color:red}

## compressing done in 13 ms

.foo,.test{color:red}

Using --debug option adds stack trace to CSS parse error output. That can help to find out problem in parser.

> echo '.a { color }' | csso --debug

Parse error <stdin>: Colon is expected
    1 |.a { color }
------------------^
    2 |

/usr/local/lib/node_modules/csso/lib/cli.js:243
                throw e;
                ^

Error: Colon is expected
    at parseError (/usr/local/lib/node_modules/csso/lib/parser/index.js:54:17)
    at eat (/usr/local/lib/node_modules/csso/lib/parser/index.js:88:5)
    at getDeclaration (/usr/local/lib/node_modules/csso/lib/parser/index.js:394:5)
    at getBlock (/usr/local/lib/node_modules/csso/lib/parser/index.js:380:27)
    ...

License

MIT