Bredon is a modern, specification-driven CSS value compiler in JavaScript.
It's parser uses very detailed nodes and provides as much information as possible.
The generated AST (Abstract Syntax Tree) is simple and readable which allows efficient and straight-forward transormation. It automatically outputs formatted CSS values.
Support Robin Frischmann's work on Fela and its ecosystem (Bredon) directly via Patreon.
Or support us on Open Collective to fund community work. This also includes Bredon as well.
Thank you to all our backers!
yarn add bredonAlternatively use npm i --save bredon.
I am heavily involved in the whole CSS in JS movement with Fela and Elodin as well as inline-style-prefixer. While writing Elodin, a plugin-based style object linter, I struggled to do complex value validation and value transformation. As CSS values are just plain strings, we do not have any meaningful types.
But, in order to perform efficient validation and transformation, we have to parse CSS values into useful type-aware components. That's where Bredon joins the game. It uses a specification-driven value parser that provides the required degree of accuracy and detail.
Bredon also serves as a personal project to learn and understand how compilers work.
I heavily used James Kyle's the-super-tiny-compiler to build Bredon. It follows the exact same steps as any other compiler does:
- First of all we read the input, one by one, and generate tokens
- Then we parse these tokens into syntactic nodes, also know as AST
- (optional) We may now traverse the AST and transform nodes
- Finally we generate a new CSS value using the transformed AST
import { parse, generate } from 'bredon'
const input = '10px solid rgba(255, 0, 255, 0.55)'
const ast = parse(input)
ast === {
type: 'ValueList',
body: [{
type: 'Value',
important: false,
body: [{
type: 'Dimension',
unit: 'px',
value: {
type: 'Integer',
negative: false,
value: 10
}
}, {
type: 'Identifier',
value: 'solid'
}, {
type: 'FunctionExpression',
callee: 'rgba',
params: [{
type: 'Integer',
negative: false,
value: 255
}, {
type: 'Integer',
negative: false,
value: 0
}, {
type: 'Integer',
negative: true,
value: 255
}, {
type: 'Float',
negative: false,
fractional: 0.55,
integer: 0,
}]
}]
}]
}
const output = generate(ast)
console.log(output)
// => 10px solid rgba(255, 0, 255, 0.55)
// parsing and generation can be combined
const output = compile(input)Bredon's most powerful part is its extendable plugin system.
Plugins are used to analyze and transform AST nodes.
| Plugin | Version | Size | Description |
|---|---|---|---|
| calc |  |
 |
Precalculate calc() expression as much as possible |
| case |  |
 |
Normalize letter case for all identifiers |
| color |  |
 |
Manipulate, normalize and minify CSS color values |
| initial |  |
 |
Replace, normalize and minify initial values |
| precision |  |
 |
Normalize decimal number precision |
| remove-unit |  |
|
Remove unnecessary value units |
| trim-hex |  |
 |
Minify hex color values if possible |
| unit |  |
 |
Convert, normalize and minify unit values |
To use Bredon within your project, you will need to somehow integrate the compiler into your workflow.
Currently, we support to options to do so. You can either use Bredon with your existing CSS codebase using PostCSS.
For JavaScript-based styling solutions (CSS in JS), there is Elodin which can be configured to auto-fix styles.
You can also use bredon-minify and bredon-validate as a stand-alone plugin for PostCSS:
Join us on Gitter.
We highly appreciate any contribution.
We also love to get feedback.
Bredon is licensed under the MIT License.
Documentation is licensed under Creative Common License.
Created with ♥ by @rofrischmann.
