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    Free-Style is designed to make CSS easier and more maintainable by using JavaScript.


    npm install free-style --save


    There's a great presentation by Christopher Chedeau you should check out.

    Solved by using CSS in JS

    • No global variables (What and where is .button? Why is it conflicting?)
    • Defined dependency systems (CommonJS, Require.js, <script />)
    • Dead code elimination automatically removes unused styles
    • Minification through JavaScript tooling
    • Shared constants and reusable styles
    • Every style is isolated, tested and namespaced to the JS component
    • Extensible - everything from Math to color manipulation already exists!

    Also solved with Free-Style

    • Works with third-party DOM components (You can nest regular .class-name in your styles)
    • Consistently generates styles and class names, and will automatically merge duplicate styles
    • Develop components alongside the style (No more hunting CSS files for estranged ul > li > a)
    • Create universal applications and serve styles for only the components rendered (see React Free-Style)
    • Use the CSS you already know ({ '&:hover': { ... } })
    • Automatically namespace @-rule styles ({ '@media (min-width: 500px)': { ... } })
    • Overload CSS properties using arrays ({ backgroundColor: ['red', 'linear-gradient(to right, red 0%, blue 100%)'] })
    • Small and powerful API that works with any ecosystem (~360 SLOC)

    But How?

    Free-Style generates a consistent hash from the style, after alphabetical property ordering and formatting, to use as the class name. This allows duplicate styles to automatically be merged on duplicate hashes. Every style is "registered" and assigned to a variable, which gets the most out of linters that will warn on unused variables and features like dead code minification. Using "register" returns the class name used for the Style instance and style instances (returned by create()) can be merged together at runtime to output only the styles on page (see React Free-Style). Styles should usually be created outside of the application run loop (e.g. render()) so the CSS string and hashes are only generated once.

    Ways to Use

    • react-free-style - React implementation that renders styles on the current page (for universal apps)
    • typestyle - Popular type-safe interface for working with CSS
    • stylin - Simplest abstraction for creating styles, rules, and keyframes, and keeps <style /> in sync
    • easy-style - Light-weight singleton API for browsers and node
    • i-css - Library for writing CSS with literal objects
    • This module! - Manually create, compose and manipulate style instances


    var FreeStyle = require('free-style')
    // Create a stylesheet instance.
    var Style = FreeStyle.create()
    // Register a new style, returning a class name to use.
    var backgroundStyle = Style.registerStyle({
      backgroundColor: 'red'
    }) //=> "f14svl5e"
    // Inject `<style>` into the `<head>`.
    var styleElement = document.createElement('style')
    styleElement.textContent = Style.getStyles()
    // Render the style by using the class name.
      <div className={backgroundStyle}>Hello world!</div>,


    var buttonStyle = Style.registerStyle({
      backgroundColor: 'red',
      padding: 10
    console.log(buttonStyle) //=> "f65pi0b"

    Tip: The string returned by registerStyle is a unique hash of the content and is used as the class in HTML.

    Overload CSS Properties

      background: [
        '-moz-linear-gradient(left, red 0%, blue 100%)',
        '-webkit-linear-gradient(left, red 0%, blue 100%)',
        '-o-linear-gradient(left, red 0%, blue 100%)',
        '-ms-linear-gradient(left, red 0%, blue 100%)',
        'linear-gradient(to right, red 0%, blue 100%)'
    }) //=> "f1n85iiq"

    Nest Rules

      color: 'red',
      '@media (min-width: 500px)': {
        color: 'blue'
    }) //=> "fk9tfor"

    Nest Selectors

      color: 'red',
      '.classname': {
        color: 'blue'
    }) //=> "fc1zv17"

    Parent Selector Reference

      color: 'red',
      '&:hover': {
        color: 'blue'
    }) //=> "f1h42yg6"

    Tip: The ampersand (&) will be replaced by the parent selector at runtime. In this example, the result is .f1h42yg6:hover.

    Tip: The second argument to registerStyle, registerKeyframes and registerHashRule is a "display name". The display name will be used as the class name prefix in development (process.env.NODE_ENV !== 'production').

    Use JavaScript

    var extend = require('xtend')
    var ellipsisStyle = {
      whiteSpace: 'nowrap',
      overflow: 'hidden',
      textOverflow: 'ellipsis'
    var redEllipsisStyle = Style.registerStyle(extend(
        color: 'red'
    )) //=> "fvxl8qs"

    Tip: This is a shallow extend example. There are modules on NPM for deep extending objects. You can also take advantage of new JavaScript features, such as const and computed properties:

    const mediaQuery = '@media (min-width: 400px)'
    const style = Style.registerStyle({
      backgroundColor: 'red',
      [mediaQuery]: {
        backgroundColor: 'pink'

    Unique Style Ouput

    Sometimes you need to skip the de-duping behaviour of free-style. Use the IS_UNIQUE export and enforce every style to be output separately:

      color: 'blue',
      '&::-webkit-input-placeholder': {
        color: `rgba(0, 0, 0, 0)`,
        [FreeStyle.IS_UNIQUE]: true
      '&::-moz-placeholder': {
        color: `rgba(0, 0, 0, 0)`,
        [FreeStyle.IS_UNIQUE]: true
      '&::-ms-input-placeholder': {
        color: `rgba(0, 0, 0, 0)`,
        [FreeStyle.IS_UNIQUE]: true
    }) //=> "f13byakl"
    Style.getStyles() //=> ".f13byakl{color:blue}.f13byakl::-webkit-input-placeholder{color:rgba(0, 0, 0, 0)}.f13byakl::-moz-placeholder{color:rgba(0, 0, 0, 0)}.f13byakl::-ms-input-placeholder{color:rgba(0, 0, 0, 0)}"


    var colorAnimation = Style.registerKeyframes({
      from: { color: 'red' },
      to: { color: 'blue' }
    }) //=> "h1j3ughx"
    var style = Style.registerStyle({
      animationName: colorAnimation,
      animationDuration: '1s'
    }) //=> "fibanyf"

    Tip: The string returned by registerKeyframes the name of the animation, which is a hash of the rule (you can also add a "display name" in development).

    Hash Rule

    Hashed rules are what registerKeyframes uses internally. It accepts a prefix and the styles object, which will create a rule using prefix + hash. Conveniently, the same contents will generate the same hash so you can register vendor-specific rules using the same hash.

    var keyframes = {
      from: {
        color: 'blue'
      to: {
        color: 'red'
    var animation1 = Style.registerHashRule('@keyframes', keyframes) //=> "f1dz2mpx"
    var animation2 = Style.registerHashRule('@-webkit-keyframes', keyframes) //=> "f1dz2mpx"


    Style.registerRule('@font-face', {
      fontFamily: '"Bitstream Vera Serif Bold"',
      src: 'url("")'
    Style.registerRule('@media print', {
      body: {
        color: 'red'
    Style.registerRule('body', {
      margin: 0,
      padding: 0

    CSS Object

      body: {
        margin: 0,
        padding: 0,
        '@print': {
          color: '#000'
      h1: {
        fontSize: '2em'

    CSS String

    Style.getStyles() //=> ".f65pi0b{background-color:red;padding:10px}"

    Useful Libraries

    Implementor Details

    Custom Hash Algorithm

    Initialize Free-Style with a custom CSS class generator.

    create(hashFunction) //=> `FreeStyle.FreeStyle`


    Debug mode can changed programmatically using the second argument to create([hash [, debug]). It defaults to the value of process.env.NODE_ENV !== 'production'.


    Free-Style provides two methods for detecting style changes. First is a changeId property, incremented every time a change occurs.

    const Style = create()
    const prevChangeId = Style.changeId
    Style.registerStyle({ color: 'red' })
    if (Style.changeId !== prevChangeId) {}

    Second, the third argument to create() is a map of change function handlers. All functions are required:

    • add (style: Container<any>, index: number): void
    • change (style: Container<any>, oldIndex: number, newIndex: number): void
    • remove (style: Container<any>, index: number): void

    All classes implement Container, so you can getStyles(), getIdentifier() or use id.


    FreeStyle.FreeStyle // Similar to writing a CSS file, holds styles and rules - returned from `create()`.
    FreeStyle.Style // Styles hold the CSS string and a generate a consistent hash of their contents.
    FreeStyle.Rule // Rules are lighter-weight containers that can be nested inside `FreeStyle` instances.
    FreeStyle.Selector // Selectors hold the CSS selector and can be nested inside `Style` instances.
    FreeStyle.Cache // `FreeStyle`, `Style` and `Rule` all extend the cache which maintains reference counts.

    Other Properties and Methods

    var ChildStyle = Style.create()
    Style.merge(ChildStyle) // Merge the child styles into the current instance.
    Style.unmerge(ChildStyle) // Unmerge the child styles from the current instance.

    Legacy Browsers

    To support legacy browsers (<= IE8) you'll need to polyfill some ES5 features, such as Object.keys, Object.create(null) and Array.isArray.




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