Parsing and Stringifying CSS

If you want to parse CSS to a abstract syntax tree (AST) then there are two solutions you might want to consider:

• reworkcss/css
• deno_css

reworkcss/css was written originally for Node.js but work well when consumed from a CDN. Importing from esm.sh also automatically combines the type definitions from DefinitelyTyped. It should be noted though that types on DefinitelyTyped are not very good as many union types that should be tagged union types are just union types which leave the types very ambiguous and require a lot of type casting.

Also, if you want to take an AST and generate CSS, reworkcss/css also provides capability to stringify the AST it generates.

deno_css is authored in TypeScript specifically for Deno and is available on deno.land/x.

Basic example with reworkcss/css

In this example, we will parse some CSS into an AST and make a modification to the background declaration of the body rule, to change the color to white. Then we will stringify the modified CSS AST and output it to the console:

import * as css from "https://esm.sh/css@3.0.0";
import { assert } from "https://deno.land/std@0.183.0/testing/asserts.ts";

declare global {
  interface AbortSignal {
    reason: unknown;
  }
}

const ast = css.parse(`
body {
  background: #eee;
  color: #888;
}
`);

assert(ast.stylesheet);
const body = ast.stylesheet.rules[0] as css.Rule;
assert(body.declarations);
const background = body.declarations[0] as css.Declaration;
background.value = "white";

console.log(css.stringify(ast));

A basic example with deno_css

In this example, we will parse some CSS into an AST and log out the background declaration of the body rule to the console.

import * as css from "https://deno.land/x/css@0.3.0/mod.ts";

const ast = css.parse(`
body {
  background: #eee;
  color: #888;
}
`);

const [body] = ast.stylesheet.rules;
const [background] = body.declarations;

console.log(JSON.stringify(background, undefined, "  "));