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A Node.js utility for safely rewriting URLs in CSS code
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CSS URL Utilities

There are many reasons why you would want to systematically replace URLs in CSS code: to convert them into data URIs, to point them to a CDN, to replace a filename with an auto-generated one, and so on. This utility helps by parsing out the URLs in a given string of CSS code and allowing you to replace them with any value you choose. The resulting CSS code is exactly the same as the original except that the URLs have been replaced according to your preferences.

This library contains utilities to help manipulate and change CSS URLs.

CSS URL Rewriter

The CSS URL rewriter uses a CSS tokenizer to safely find all CSS URLs. This makes any change completely safe because there is no reliance on regular expressions to pull URLs out of CSS.

Usage

var URLRewriter = require("cssurl").URLRewriter;

var rewriter = new URLRewriter(function(url) {
    // automatically append a query string with a unique value to bust caches
    return url + "?v=" + Date.now();
});

var result = rewriter.rewrite(cssCode);

As the CSS URL rewriter goes through the CSS code, it will call the function passed to the CSSURLRewriter constructor and pass in each URL that it finds. The url is the URL as found in the CSS code with any quotes and surrounding whitespace removed (it does not contain the url()). You can then inspect the URL, modify it however you want, and return the value you want to use in its place.

Limitations

The CSS URL Rewriter will only replace URLs represented as URL tokens, that means it must be in the form url(foo.css) and not just "foo.css", as is allowed in some parts of CSS.

CSS URL Rewrite Stream

The CSS URL rewrite stream uses the URL rewriter inside of a stream so you can easily pipe code to and from.

Usage

var URLRewriteStream = require("cssurl").URLRewriteStream;

fs.createReadStream("my.css").pipe(new URLRewriteStream(function(url) {
    // automatically append a query string with a unique value to bust caches
    return url + "?v=" + Date.now();
})).pipe(fs.createWriteStream("my-new.css"));

CSS URL Translator

The CSS URL translator is a utility that can translate CSS URLs relative to different CSS files. Sometimes you might want to move a CSS file, for example from css/sprites/foo.css to css/sprites.css. When you do that, any relative URLs in the CSS file will no longer be accurate. The CSS URL translator, when used in conjunction with the CSS URL rewriter, makes it easy to make these changes by automatically calculating the new URL path. It's also smart enough not to translate any non-relative URLs.

Usage

var URLTranslator = require("cssurl").URLTranslator;

var translator = new URLTranslator();
var result = translator.translate("../../img/foo.png", "css/sprites/foo.css", "css/sprites.css");

console.log(result);    // "../img/foo.png"

Development

In order to run tests, clone this repository and then run:

$ npm i
$ npm test

Copyright and License (BSD3)

Copyright 2014 Nicholas C. Zakas. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

  3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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