css-patch

Generating CSS patches (just like a diff).

Use cases

Themes generation

The easiest way to make a new theme is to copy the file and change some stuff or, if you use a preprocessor (such as SCSS, Less, etc.), change some variables and get a new stylesheet.

But serving files with big amount of the same code is not a good idea, so this is when css-patch can help you.

You can pass 2 stylesheets (original/base and expected) to generateCSSPatch and get a new stylesheet. This new stylesheet is intended to be applied after original one and will have the same effect as if you applied expected one. In other words, the new stylesheet will consist of the resulting "overloads" for the original one.

Extracting difference

Imagine that you have two versions of the same CSS stylesheet.

By using this module you can get the difference between them.

Install

Install via yarn:

yarn add css-patch

Install via npm:

npm i css-patch

Docs

Read the docs on GitHub pages.

For advanced usage see the docs for transformCSS function and CSSTransformerBase class.

Possible caveats

unset

Declarations missing in expected stylesheet, but present in original one, will be set to unset.

Combined rule orders

Logically the same but with a different order combined rules (e.g..a,.b and .b,.a) will be considered as a different rules.

Merged rules

Rules with the same name will have their declarations merged with each other, overriding previous declarations in the order they appear.

For example .a{a:1;c:3;}.a{a:2;b:2;} will be treated as .a{a:2;b:2;c;3}.

Sorting

Declarations are sorted alphabetically.

Usage example

Import

CommonJS

const { generateCSSPatch, } = require('css-patch');

ES6

import { generateCSSPatch, } from 'css-patch';

Use

console.log(
	generateCSSPatch(`
a { same: value; missing: value; }
b { different: original_value; }
c { same: rule; }
missing_rule { missing: value; }
		`, `
a { same: value; }
b { different: new_value; }
c { same: rule; }
		`
	)
); // 'a{missing:unset;}b{different:new_value;}missing_rule{missing:unset;}'