css-tokens

Overview

A regex that tokenizes CSS.

var cssTokens = require("css-tokens")

// Tokenize a whole string of CSS:
cssString.match(cssTokens)
// [".foo", "{", "prop", ":", " ", "foo", ";", "}", "\n", ...]

// Rename the class `foo` to `bar`:
cssString.replace(cssTokens, function(token) {
  if (token === ".foo") {
    token = "bar"
  }
  return token
})
// [".bar", "{", "prop", ":", " ", "foo", ";", "}", "\n", ...]

Installation

npm install css-tokens

var cssTokens = require("css-tokens")

Usage

cssTokens

A regex with the g flag that matches CSS tokens.

The regex always matches, even invalid CSS and the empty string. For example, cssTokens.exec(string) never returns null.

The next match is always directly after the previous. Each token has its own capturing group.

cssTokens.names

An array of names for each token, in the capturing group order.

Invalid code handling

Unterminated strings are still matched as strings. CSS strings cannot contain (unescaped) newlines, so unterminated strings simply end at the end of the line.

Unterminated multi-line comments are also still matched as comments. They simply go on to the end of the string.

Unterminated unquoted urls are also still matched as unquoted urls. They continue as long as there are valid characters.

Invalid ASCII characters have their own capturing group.

Limitations

Tokenizing CSS using regexes—in fact, one single regex—won’t be perfect. But that’s not the point either.

@ or . followed by a single -

Ideally, @- and .- (followed by a non-name character) would be matched as invalid + operator, but they are in fact matched as names. This could be fixed, but isn’t to simplify the regex. It doesn’t really matter.

Note that #- is actually allowed by the spec.

Quoted vs. unquoted urls

The following is hardly a “limitation”, but could be mentioned:

url(http://www.w3.org/2000/svg)
url('http://www.w3.org/2000/svg')

The first line is matched as one single token (unquotedUrl), while the second is matched as four (name + punctuation + string + punctuation). This could be fixed, but isn’t to simplify the regex.

Build

index.js is generated by running node generate-index.js. The regex is written in regex.coffee. Don’t worry, you don’t need to know anything about CoffeeScript: regex.coffee should be kept as simple as possible. CoffeeScript is only used for its block regexes, which have the following benefits:

• Insignificant whitespace.
• Comments.
• No need to escape slashes.
• No need to double-escape everything (as opposed to using RegExp("regex as a string. One backslash: \\\\")).
• Plenty of syntax highlighters available.

Everything else is written in JavaScript.

License

The X11 (“MIT”) License.