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JavaScript Style Sheet - Instead of putting programming in CSS, it puts CSS in a programming language.
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JavaScript StyleSheet - JS3

Instead of putting programming in CSS, it puts CSS in a programming language.


As more and more development is moving towards client side, different opportunities are opening up and traditional styles of doing everything are undergoing drastic changes. CSS definition is one such case.

CSSes are style definitions which are static in nature, but with pre-processors like LESS and SASS, adding dynamism to CSS becomes much easier. Although limited to design-time, with pre-processors, static style sheets get some life in form of variables, mixins, inheritance, etc. However once processed, they again become static styles. Therefore all such liveliness still remains inside the xxSS execution engine.

With the help of javascript, styles can be manipulated at run-time, both at element level (e.g., using $.css(...)) as well as global level (e.g., using document.styleSheets). However updating values using former approach changes specificity, while using later approach is tedious and raw.

This is where JS3 brings the difference. It creates live CSS. A live CSS is a javascript object that transparently writes/updates CSS (in browser) in real-time, as you play with this object. You get the best of both worlds, LESS, SASS type design-time dynamism that can be applied at run-time using plain javascript.

JS3 can load predefined *.js3 files (comparable to *.css files) or can even define a new CSS on the fly using pure javascript.


  • Pure JavaScript
  • No external dependencies in core engine
  • Supports all CSS features as-is (including experimental ones)
  • Hierarchal definition of selectors along with mixin support reduces amount of code to be written for lengthy and repetitive CSS scenarios
  • Future proof syntax, anything that comes in future CSS structure, when not supported directly can be written-to as is
  • Almost zero learning curve (if you know JavaScript and know how to write CSS, you already know 99% of JS3)
  • No build steps (its not a pre-processor)
  • Live CSS (updates CSS transparently in DOM, without any flicker)
  • Open extension model to extend JS3 objects for further ease
  • All client-side processing, no server trips
  • No need to create additional CSS classes, and then switching them at runtime using jQuery or otherwise to see desired behavior. Instead directly play with rule, styles, or variables and see the effect instantly
  • Define styles, rules and variables, etc. only once and then share them across files
  • Define required .js3 files during definition, and let changes in referred .js3 files cascade in dependencies
  • MIT License

Getting Started

1. Install

Install using bower install JS3 or download latest release. All you need is to have JS3.min.js available, whatever approach you want to take.

2. Include

Include JS3 engine in your html page.

There are no external dependencies of the core engine of this library, therefore feel free to include in whatever order required. However this must be included before any *.js3 file or any JS3 extension is being included.

<script type="text/javascript" src="path/JS3.min.js"></script>

You may choose to include dist/JS3.core.js instead, if you don't plan to use all extensions which by default are bundled into dist/JS3.min.js file. When using dist/JS3.core.js, you can choose to include individual extensions (dist/extensions/js3.*.min.js) as per your requirement.

Loading this file will create one global variable named JS3, that will serve as the anchor for all JS3 operations.

3. Load *.js3 files

A *.js3 file can be seen as a javascript counterpart of a *.css file. With JS3, instead of writing .css you would be writing .js3 files, which are pure javascript files. These can be loaded like any other javascript file (including using any loader such as yepnope).

<script type="text/javascript" src="path/styles1.js3"></script>
<script type="text/javascript" src="path/styles2.js3"></script>

Although creating a .js3 file is recommended for clean code separation, it is possible that you write your stylesheet code directly in any javascript file of yours.

No matter how they are defined or loaded, all js3 objects will be able to see each other and can share style information at runtime.

That's all is needed to start using the power of JS3.

Create your first .js3 file

Creating a .js3 file is simply writing bunch of javascript code lines. Each js3 file gets loaded on global JS3 object by its name. Here is a quick example:

JS3.define('demo1', function() {
    // define prefixes
    prefixes('-moz-', '-webkit-');

    // define variables
    vars('lightColor', color('yellow')).tint(.9);
    vars('borderColor', color('lightgray')); 
        size: 11,
        unit: 'px'

    // define re-usable css declarations (called 'rule' here)
    rule('[allMargins] margin', 5, vars.unit);                  
    rule('[allPaddings] padding', {
        tiny: 5,
        small: 10,
        medium: 15,
        large: 25,
        xLarge: 50
    }, vars.unit).select('small');
    rule('[CodeColor] color', color('blue'));

    // define re-usable css declaration blocks (called 'style' here)
    style('basic', {
        set1: {
            color: 'black',
            'background-color': vars.lightColor
        set2: [
            rule('color', 'blue'),                      
            rule('background-color', vars.borderColor) 
    }).select(function() { return 'set1'; });

        rule('[myBorder] border', '1px dashed red'),
        rule('[allRadius] ~border-radius', 25, vars.unit)   
        rule('font-family', 'monospace')

    // write CSS, JS3 style
    $$('@charset', '"utf-8"');
    $$('@font-face', {
        'font-family': '"Bitstream Vera Serif Bold"',
        'src': 'url("")'

    $$('#root', { 
        'width': '100%'
    $$('.content li', 
    $$('#left', { 
        'width': '70%',                 
        'float': 'left'                    
    $$('#right', { 
        'width': '25%',                 
        'float': 'right'                       
            rule('padding-bottom', 20, vars.unit)

    $$('&/* some comments */');

    // ends definition and loads css

Above defined .js3 will eventually generate following .css

@charset "utf-8";
@font-face {
    font-family: "Bitstream Vera Serif Bold";
    src: url("");
body {
    color: black;
    background-color: rgba(255,255,230,1);
    padding: 10px;
    margin: 5px;
#root {
    width: 100%;
.content li {
    font-family: monospace;
#left {
    width: 70%;
    float: left;
#right {
    width: 25%;
    float: right;
#right div {

#right .widget {
    padding-bottom: 20px;
/* some comments */

Check Creating your first .js3 file guide for detailed and step-by-step rundown of key concepts shown here and more.

Using the power of JS3

JS3 global object provides access to all core functionalists as well as all loaded style sheets. Some quick samples to give you an idea of various possibilities are:

Change variable's value:


Perform operations:


Change style rule value, from predefined set:'large');

Turn a style rule off:;

Add new (pre-defined) rule:


Across files re-usability: Access definitions from other files into current file.

JS3.define('demo2', ['demo1'], function() {

            rule('overflow', 'auto'),
            rule('height', 50, demo1.vars.unit)


Perform batch changes:


Remain informed:

JS3.onChange('myHandler', function(e) {

// e.css holds css object where changes are done
// e.type holds the type of change


Possibilities are many. Check out the documentation to see what all is available.


JS3 documentation is available here.

Release History

See the changelog here.

Contributing to JS3

Community contributions will made JS3 a better specification and framework. If you are interested in contributing, please follow these simple guidelines.

Use stackoverflow for questions. Issues should be opened if you find a problem or have an enhancement request.

Supply a working sample against the enhancement.

Similar Projects

There are several projects which are on similar lines, i.e., CSS and JavaScript together. However unlike JS3, none of below mentioned, do it in totality and provide an end-to-end seamless experience for stylesheet processing.

If you find something else that is coming up on similar lines, please share your findings and I will incorporate it here for everyone's reference.


Copyright (C) 2014 Vikas Burman. All rights reserved.

Licensed under the terms of the MIT license. You are free to use JS3 under any open source or commercial project, as long as this copyright header is left intact.

Disclaimer: JS3 is authored by me (Vikas Burman). The concepts and opinions found here, as well as in code, are my own and do not represent my employers (past, current or future) in any ways.

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