Modular CSS preprocessing with rework
Several months ago I started a project named Rework, a very fast, simple, flexible, and modular CSS preprocessor. The biggest and most obvious question I get is how this tool compares to something like Stylus, LESS, or Sass, and why would you want to use it.
The simple answer is that Rework caters to a different audience, and provide you the flexibility to craft the preprocessor you want, not the choices the author(s) have force on you.
Our goal with Rework contrasts the others, as it does not provide a higher level language within the CSS documents, Rework’s goal is to make those constructs unnecessary, being the most transparent CSS pre-processor out there.
Speed
Rework was designed to be simple and fast out of the box, without implementing complex caching models allowing everyone to hack on Rework itself or associate plugins easily.
Powering rework is a css parser written in JavaScript that may be used with node.js or in the browser. On the other end there is the css compiler which accepts the AST from css-parse, outputting CSS.
So where does Rework come in? Rework is the plugin and transformation engine that sits in-between these two tools. The AST is manipulated by Rework and its plugins (or user-defined plugins), which is then passed to the compiler.
Because these transformations are performed in JavaScript and not in a specialized preprocessor language they are simple to implement and efficient.
Let’s check out what it can do!
Modularity & Flexibility
Before diving into the plugins bundled with Rework, let’s take a look at how they can be applied. Rework’s API is very simple, you can specify vendor prefixes with .vendors(), which all plugins have access to, or you may pass specific vendor prefixes to most plugins themselves. Plugins are passed to a .use() method, and then finally the CSS output is returned with .toString(). In practice this looks something like:
var rework = require('rework');
var css = rework('string of css here')
.vendors(['-webkit-', '-moz-'])
.use(rework.prefixValue('linear-gradient'))
.use(rework.prefixValue('radial-gradient'))
.use(rework.prefixValue('transform'))
.use(rework.vars())
.use(rework.colors())
.toString()
Out of the box rework provides plugins for the following, which may be mixed and matched as you wish:
- media macros — define your own @media queries
- ease — several additional easing functions
- at2x — serve high resolution images
- prefix — add vendor prefixes to properties
- prefixValue — add vendor prefixes to values
- prefixSelectors — add prefixes to selectors
- opacity — add IE opacity support
- url — rewrite
url()s with a callback function - vars — add css variable support
- keyframes — add @keyframe vendor prefixing
- colors — add colour helpers like
rgba(#fc0, .5) - references — add property references support
height: @widthetc - mixin — add custom property logic with mixing
- extend — add
extend: selectorsupport
Let’s look at some examples!
Vendor prefixes
The prefix, prefixValue, and keyframes plugins make vendor prefixing extremely simple. Here the prefix plugin is applied to only two properties for illustration:
var rework = require('..')
var read = require('fs').readFileSync
var css = rework(read('examples/prefix.css', 'utf8'))
.vendors(['-webkit-', '-moz-'])
.use(rework.prefix('border-radius'))
.use(rework.prefix('box-shadow'))
.toString()
console.log(css)
With the prefix.css file containing the following CSS:
.button {
border-radius: 5px;
box-shadow: inset 0 0 1px white;
}
Rework yields the following prefixed output:
.button {
-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 5px;
-webkit-box-shadow: inset 0 0 1px white;
-moz-box-shadow: inset 0 0 1px white;
box-shadow: inset 0 0 1px white
}
Extending
The extend plugin adds support for a special property named extend, which propagates the selector back up the AST so that the styles are applied without duplication. For example here’s a contrived green join button implementation:
button {
padding: 5px 10px;
border: 1px solid #eee;
border-bottom-color: #ddd;
}
.green {
background: green;
padding: 10px 15px
}
a.join {
extend: button;
extend: .green;
padding: 20px;
}
With this plugin enabled both of the extend properties are gone, and you’re left with the CSS you might expect:
button,
a.join {
padding: 5px 10px;
border: 1px solid #eee;
border-bottom-color: #ddd
}
.green,
a.join {
background: green;
padding: 10px 15px
}
a.join {
padding: 20px
}
Better rgba()
Ever had a color hex and then wanted to alter the alpha channel? Then you probably know how annoying this is with CSS. The colors plugin allows you to pass hex values to rgba(), for example rgba(#c00, .5) which is then compiled to rgba(204,0,0,0.5).
Writing your own plugins
Writing plugins for Rework is simple, suppose for example you want the ability to create your own properties, here expanding single-line position properties:
#logo {
absolute: top left;
}
#logo {
relative: top 5px left;
}
#logo {
fixed: top 5px left 10px;
}
Into the valid CSS shown below:
#logo {
position: absolute;
top: 0;
left: 0
}
#logo {
position: relative;
top: 5px;
left: 0
}
#logo {
position: fixed;
top: 5px;
left: 10px
}
The AST css-parse provides you is made up of simple objects and arrays, making it extremely easy to manipulate without extra knowledge of how the nodes are constructed or strange internal APIs. In the following plugin function we walk the declarations, check if the property is one of the positions, parse the value by splitting on whitespace and then inject the new css properties.
function positions() {
var positions = ['absolute', 'relative', 'fixed'];
return function(style){
rework.visit.declarations(style, function(declarations){
declarations.forEach(function(decl, i){
if (!~positions.indexOf(decl.property)) return;
var args = decl.value.split(/\s+/);
var arg, n;
// remove original
declarations.splice(i, 1);
// position prop
declarations.push({
property: 'position',
value: decl.property
});
// position
while (args.length) {
arg = args.shift();
n = parseFloat(args[0]) ? args.shift() : 0;
declarations.push({
property: arg,
value: n
});
}
});
});
}
}
To use this plugin you would simply pass it to .use():
var css = rework('#logo { absolute: top left; }')
.use(positions())
.toString()
Significant whitespace
Since CSS has a relatively simple grammar significant whitespace can help improve your productivity without turning the whole thing into an unreadable mess, this is especially true since Rework does not provide the higher level language constructs, which can get lost in the indentation. This is where css-whitespace comes in! It lets you write things like:
ul
li
background: #eee
&:hover
background: white
&:active
background: #ddd
Which yields:
ul li:hover {
background: white;
}
ul li:active {
background: #ddd;
}
ul li {
background: #eee;
}
Future
In the near future we’ll be providing a more intuitive way to apply all or large chunks of the functionality Rework provides without manually adding all of the plugins, as well as improving the rework(1) executable.
