css-parser

CSS parser and minifier for node and the browser

Installation

From npm

$ npm install @tbela99/css-parser

from jsr

$ deno add @tbela99/css-parser

Features

• no dependency
• partial css validation based upon mdn-data: at-rules and selectors validation
• fault-tolerant parser, will try to fix invalid tokens according to the CSS syntax module 3 recommendations.
• fast and efficient minification without unsafe transforms, see benchmark
• minify colors: color(), lab(), lch(), oklab(), oklch(), color-mix(), light-dark(), system colors and relative color
• generate nested css rules
• convert nested css rules to legacy syntax
• generate sourcemap
• compute css shorthands. see supported properties list below
• css transform functions minification
• evaluate math functions: calc(), clamp(), min(), max(), etc.
• inline css variables
• remove duplicate properties
• flatten @import rules

Playground

Try it online

Exports

There are several ways to import the library into your application.

Node exports

import as a module

import {transform} from '@tbela99/css-parser';

// ...

Deno exports

import as a module

import {transform} from '@tbela99/css-parser';

// ...

import as a CommonJS module

const {transform} = require('@tbela99/css-parser/cjs');

// ...

Web export

Programmatic import

import {transform} from '@tbela99/css-parser/web';

// ...

Javascript module from cdn

<script type="module">

    import {transform} from 'https://esm.sh/@tbela99/css-parser@1.0.0/web';


    const css = `
    .s {

    background: color-mix(in hsl, color(display-p3 0 1 0) 80%, yellow);
}
    `;

    console.debug(await transform(css).then(r => r.code));

</script>

Javascript module

<script src="dist/web/index.js" type="module"></script>

Single Javascript file

<script src="dist/index-umd-web.js"></script>

Transform

Parse and render css in a single pass.

Usage

transform(css, transformOptions: TransformOptions = {}): TransformResult

Example

import {transform} from '@tbela99/css-parser';

const {ast, code, map, errors, stats} = await transform(css, {minify: true, resolveImport: true, cwd: 'files/css'});

TransformOptions

Include ParseOptions and RenderOptions

ParseOptions

Minify Options

• minify: boolean, optional. default to true. optimize ast.
• pass: number, optional. minification pass. default to 1
• nestingRules: boolean, optional. automatically generated nested rules.
• expandNestingRules: boolean, optional. convert nesting rules into separate rules. will automatically set nestingRules to false.
• removeDuplicateDeclarations: boolean, optional. remove duplicate declarations.
• computeTransform: boolean, optional. compute css transform functions.
• computeShorthand: boolean, optional. compute shorthand properties.
• computeCalcExpression: boolean, optional. evaluate calc() expression
• inlineCssVariables: boolean, optional. replace some css variables with their actual value. they must be declared once in the :root {} or html {} rule.
• removeEmpty: boolean, optional. remove empty rule lists from the ast.

Validation Options

• validation: boolean, optional. enable strict css validation using (mdn data)[https://github.com/mdn/data]. only the selector is validated at this time.
• lenient: boolean, optional. ignore unknown at-rules, pseudo-classes and declarations.

Sourcemap Options

• src: string, optional. original css file location to be used with sourcemap, also used to resolve url().
• sourcemap: boolean, optional. preserve node location data.

Ast Traversal Options

• visitor: VisitorNodeMap, optional. node visitor used to transform the ast.

Urls and @import Options

• resolveImport: boolean, optional. replace @import rule by the content of the referenced stylesheet.
• resolveUrls: boolean, optional. resolve css 'url()' according to the parameters 'src' and 'cwd'

Misc Options

• removeCharset: boolean, optional. remove @charset.
• cwd: string, optional. destination directory used to resolve url().
• signal: AbortSignal, optional. abort parsing.

RenderOptions

Minify Options

• beautify: boolean, optional. default to false. beautify css output.
• minify: boolean, optional. default to true. minify css values.
• withParents: boolean, optional. render this node and its parents.
• removeEmpty: boolean, optional. remove empty rule lists from the ast.
• expandNestingRules: boolean, optional. expand nesting rules.
• preserveLicense: boolean, force preserving comments starting with '/*!' when minify is enabled.
• removeComments: boolean, remove comments in generated css.
• convertColor: boolean, convert colors to hex.

Sourcemap Options

• sourcemap: boolean, optional. generate sourcemap

Misc Options

• indent: string, optional. css indention string. uses space character by default.
• newLine: string, optional. new line character.
• output: string, optional. file where to store css. url() are resolved according to the specified value. no file is created though.
• cwd: string, optional. destination directory used to resolve url().

Parsing

Usage

parse(css, parseOptions = {})

Example

const {ast, errors, stats} = await parse(css);

Rendering

Usage

render(ast, RenderOptions = {});

Examples

Rendering ast

import {parse, render} from '@tbela99/css-parser';

const css = `
@media screen and (min-width: 40em) {
    .featurette-heading {
        font-size: 50px;
    }
    .a {
        color: red;
        width: 3px;
    }
}
`;

const result = await parse(css, options);

// print declaration without parents
console.error(render(result.ast.chi[0].chi[1].chi[1], {withParents: false}));
// -> width:3px

// print declaration with parents
console.debug(render(result.ast.chi[0].chi[1].chi[1], {withParents: true}));
// -> @media screen and (min-width:40em){.a{width:3px}}

Merge similar rules

CSS

.clear {
    width: 0;
    height: 0;
    color: transparent;
}

.clearfix:before {

    height: 0;
    width: 0;
}

import {transform} from '@tbela99/css-parser';

const result = await transform(css);

Result

.clear, .clearfix:before {
    height: 0;
    width: 0
}

.clear {
    color: #0000
}

Automatic CSS Nesting

CSS

const {parse, render} = require("@tbela99/css-parser/cjs");

const css = `
table.colortable td {
 text-align:center;
}
table.colortable td.c {
 text-transform:uppercase;
}
table.colortable td:first-child, table.colortable td:first-child+td {
 border:1px solid black;
}
table.colortable th {
 text-align:center;
 background:black;
 color:white;
}
`;

const result = await parse(css, {nestingRules: true}).then(result => render(result.ast, {minify: false}).code);

Result

table.colortable {
    & td {
        text-align: center;

        &.c {
            text-transform: uppercase
        }

        &:first-child, &:first-child + td {
            border: 1px solid #000
        }
    }

    & th {
        text-align: center;
        background: #000;
        color: #fff
    }
}

CSS Validation

CSS

#404 {
    --animate-duration: 1s;
}

.s, #404 {
    --animate-duration: 1s;
}

.s [type="text" {
    --animate-duration: 1s;
}

.s [type="text"]]
{
    --animate-duration: 1s;
}

.s [type="text"] {
    --animate-duration: 1s;
}

.s [type="text" i] {
    --animate-duration: 1s;
}

.s [type="text" s]
{
    --animate-duration: 1s
;
}

.s [type="text" b]
{
    --animate-duration: 1s;
}

.s [type="text" b],{
    --animate-duration: 1s
;
}

.s [type="text" b]
+ {
    --animate-duration: 1s;
}

.s [type="text" b]
+ b {
    --animate-duration: 1s;
}

.s [type="text" i] + b {
    --animate-duration: 1s;
}


.s [type="text"())]{
    --animate-duration: 1s;
}
.s(){
    --animate-duration: 1s;
}
.s:focus {
    --animate-duration: 1s;
}

with validation enabled

import {parse, render} from '@tbela99/css-parser';

const options = {minify: true, validate: true};
const {code} = await parse(css, options).then(result => render(result.ast, {minify: false}));
//
console.debug(code);

.s:is([type=text],[type=text i],[type=text s],[type=text i]+b,:focus) {
    --animate-duration: 1s
}

with validation disabled

import {parse, render} from '@tbela99/css-parser';

const options = {minify: true, validate: false};
const {code} = await parse(css, options).then(result => render(result.ast, {minify: false}));
//
console.debug(code);

.s:is([type=text],[type=text i],[type=text s],[type=text b],[type=text b]+b,[type=text i]+b,:focus) {
    --animate-duration: 1s
}

Nested CSS Expansion

CSS

table.colortable {
    & td {
        text-align: center;

        &.c {
            text-transform: uppercase
        }

        &:first-child, &:first-child + td {
            border: 1px solid #000
        }
    }

    & th {
        text-align: center;
        background: #000;
        color: #fff
    }
}

Javascript

import {parse, render} from '@tbela99/css-parser';

const options = {minify: true};
const {code} = await parse(css, options).then(result => render(result.ast, {minify: false, expandNestingRules: true}));
//
console.debug(code);

Result

table.colortable td {
    text-align: center;
}

table.colortable td.c {
    text-transform: uppercase;
}

table.colortable td:first-child, table.colortable td:first-child + td {
    border: 1px solid black;
}

table.colortable th {
    text-align: center;
    background: black;
    color: white;
}

Calc() resolution

import {parse, render} from '@tbela99/css-parser';

const css = `
a {

width: calc(100px * log(625, 5));
}
.foo-bar {
    width: calc(100px * 2);
    height: calc(((75.37% - 63.5px) - 900px) + (2 * 100px));
    max-width: calc(3.5rem + calc(var(--bs-border-width) * 2));
}
`;

const prettyPrint = await parse(css).then(result => render(result.ast, {minify: false}).code);

result

a {
    width: 400px;
}

.foo-bar {
    width: 200px;
    height: calc(75.37% - 763.5px);
    max-width: calc(3.5rem + var(--bs-border-width) * 2)
}

CSS variable inlining

import {parse, render} from '@tbela99/css-parser';

const css = `

:root {

--preferred-width: 20px;
}
.foo-bar {

    width: calc(calc(var(--preferred-width) + 1px) / 3 + 5px);
    height: calc(100% / 4);}
`

const prettyPrint = await parse(css, {inlineCssVariables: true}).then(result => render(result.ast, {minify: false}).code);

result

.foo-bar {
    width: 12px;
    height: 25%
}

CSS variable inlining and relative color

import {parse, render} from '@tbela99/css-parser';

const css = `

:root {
--color: green;
}
._19_u :focus {
    color:  hsl(from var(--color) calc(h * 2) s l);

}
`

const prettyPrint = await parse(css, {inlineCssVariables: true}).then(result => render(result.ast, {minify: false}).code);

result

._19_u :focus {
    color: navy
}

CSS variable inlining and relative color

import {parse, render} from '@tbela99/css-parser';

const css = `

html { --bluegreen:  oklab(54.3% -22.5% -5%); }
.overlay {
  background:  oklab(from var(--bluegreen) calc(1.0 - l) calc(a * 0.8) b);
}
`

const prettyPrint = await parse(css, {inlineCssVariables: true}).then(result => render(result.ast, {minify: false}).code);

result

.overlay {
    background: #0c6464
}

Node Walker

import {walk} from '@tbela99/css-parser';

for (const {node, parent, root} of walk(ast)) {

    // do something
}

AST

Comment

• typ: number
• val: string, the comment

Declaration

• typ: number
• nam: string, declaration name
• val: array of tokens

Rule

• typ: number
• sel: string, css selector
• chi: array of children

AtRule

• typ: number
• nam: string. AtRule name
• val: rule prelude

AtRuleStyleSheet

• typ: number
• chi: array of children

KeyFrameRule

• typ: number
• sel: string, css selector
• chi: array of children

Sourcemap

• sourcemap generation

Minification

• minify keyframs
• minify transform
• evaluate math functions calc(), clamp(), min(), max(), round(), mod(), rem(), sin(), cos(), tan(), asin(), acos(), atan(), atan2(), pow(), sqrt(), hypot(), log(), exp(), abs(), sign()
• multi-pass minification
• inline css variables
• merge identical rules
• merge adjacent rules
• minify colors
• minify numbers and Dimensions tokens
• compute shorthand: see the list below
• remove redundant declarations
• conditionally unwrap :is()
• automatic css nesting
• automatically wrap selectors using :is()
• avoid reparsing (declarations, selectors, at-rule)
• node and browser versions
• decode and replace utf-8 escape sequence

Computed shorthands properties

• all
• animation
• background
• border
• border-block-end
• border-block-start
• border-bottom
• border-color
• border-image
• border-inline-end
• border-inline-start
• border-left
• border-radius
• border-right
• border-style
• border-top
• border-width
• column-rule
• columns
• container
• contain-intrinsic-size
• flex
• flex-flow
• font
• font-synthesis
• font-variant
• gap
• grid
• grid-area
• grid-column
• grid-row
• grid-template
• inset
• list-style
• margin
• mask
• offset
• outline
• overflow
• padding
• place-content
• place-items
• place-self
• scroll-margin
• scroll-padding
• scroll-timeline
• text-decoration
• text-emphasis
• transition

Performance

• flatten @import

Node Transformation

Ast can be transformed using node visitors

Exemple 1: Declaration

the visitor is called for any declaration encountered

import {AstDeclaration, ParserOptions} from "../src/@types";

const options: ParserOptions = {

    visitor: {

        Declaration: (node: AstDeclaration) => {

            if (node.nam == '-webkit-transform') {

                node.nam = 'transform'
            }
        }
    }
}

const css = `

.foo {
    -webkit-transform: scale(calc(100 * 2/ 15));
}
`;

console.debug(await transform(css, options));

// .foo{transform:scale(calc(40/3))}

Exemple 2: Declaration

the visitor is called only on 'height' declarations

import {AstDeclaration, LengthToken, ParserOptions} from "../src/@types";
import {EnumToken} from "../src/lib";
import {transform} from "../src/node";

const options: ParserOptions = {

    visitor: {

        Declaration: {

            // called only for height declaration
            height: (node: AstDeclaration): AstDeclaration[] => {


                return [
                    node,
                    {

                        typ: EnumToken.DeclarationNodeType,
                        nam: 'width',
                        val: [
                            <LengthToken>{
                                typ: EnumToken.Length,
                                val: '3',
                                unit: 'px'
                            }
                        ]
                    }
                ];
            }
        }
    }
};

const css = `

.foo {
    height: calc(100px * 2/ 15);
}
.selector {
color: lch(from peru calc(l * 0.8) calc(c * 0.7) calc(h + 180)) 
}
`;

console.debug(await transform(css, options));

// .foo{height:calc(40px/3);width:3px}.selector{color:#0880b0}

Exemple 3: At-Rule

the visitor is called on any at-rule

import {AstAtRule, ParserOptions} from "../src/@types";
import {transform} from "../src/node";


const options: ParserOptions = {

    visitor: {

        AtRule: (node: AstAtRule): AstAtRule => {

            if (node.nam == 'media') {

                return {...node, val: 'all'}
            }
        }
    }
};

const css = `

@media screen {
       
    .foo {

            height: calc(100px * 2/ 15);    
    } 
}
`;

console.debug(await transform(css, options));

// .foo{height:calc(40px/3)}

Exemple 4: At-Rule

the visitor is called only for at-rule media

import {AstAtRule, ParserOptions} from "../src/@types";
import {transform} from "../src/node";

const options: ParserOptions = {

    visitor: {

        AtRule: {

            media: (node: AstAtRule): AstAtRule => {

                return {...node, val: 'all'}
            }
        }
    }
};

const css = `

@media screen {
       
    .foo {

            height: calc(100px * 2/ 15);    
    } 
}
`;

console.debug(await transform(css, options));

// .foo{height:calc(40px/3)}

Exemple 5: Rule

the visitor is called on any Rule

import {AstAtRule, ParserOptions} from "../src/@types";
import {transform} from "../src/node";

const options: ParserOptions = {

    visitor: {


        Rule(node: AstRule): AstRule {

            return {...node, sel: '.foo,.bar,.fubar'};
        }
    }
};

const css = `

    .foo {

            height: calc(100px * 2/ 15);    
    } 
`;

console.debug(await transform(css, options));

// .foo,.bar,.fubar{height:calc(40px/3)}

Exemple 6: Rule

Adding declarations to any rule

import {transform} from "../src/node";
import {AstRule, ParserOptions} from "../src/@types";
import {parseDeclarations} from "../src/lib";

const options: ParserOptions = {

    removeEmpty: false,
    visitor: {

        Rule: async (node: AstRule): Promise<AstRule | null> => {

            if (node.sel == '.foo') {

                node.chi.push(...await parseDeclarations('width: 3px'));
                return node;
            }

            return null;
        }
    }
};

const css = `

.foo {
}
`;

console.debug(await transform(css, options));

// .foo{width:3px}

---

Thanks to Jetbrains for sponsoring this project with a free license