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CSS diffing tool


For convenient testing of CSS code transforms


The tool accepts an HTML file and two CSS files: the original before your code transformation and the result of the transformation.

Then it uses PhantomJS and SlimerJS to load the HTML file twice: once inlining the "before" CSS and once with the "after" CSS. The CSS is inlined in a <style> tag.

The HTML is stripped of tags such as iframe and script that can potentially skew the visual comparison by injecting dynamic content.

The results of rendering the two HTML files are saved to two PNGs which are then compared pixel by pixel.

If they are different, a GIF animation is also created to help debug.

Finally, the "before" and "after" CSS files are copied, prettified, comment-stripped and sent to your favorite diffing app so you can easily see what changed in the CSS. The prettification is done with the Mensch CSS parser/stringifier


$ npm install cssdiff

It's up to you to install PhantomJS and/or SlimerJS. If you want just one of these, remove the other in the config.json file.

Also up to you to install ImageMagick (to create the animated GIF)

There is a config.json where you can fiddle with (or delete) the paths to the three tools, if necessary.


In code:

var cssdiff = require('../index.js');
cssdiff('index.html', 'before.css', 'after.css', function(result, msg, diff) {
  console.log(result); // `true` if all is fine 
  console.log(msg); // verbose message to help debug 
  // `diff` is the command you can execute to launch a diff program 

Command line:

$ cssdiff index.html before.css after.css diff

Example success output

All good with test/zen.html and test/before.css and test/before.css

Example failure output

ERROR! The before/after results are different
You provided test/zen.html and test/before.css and test/after.css
See these files to start debugging:
 * Generated HTML before: /path/to/tmp/ec2af394-984d-4bac-b9fb-92b4461fda1b-before.html
 * Generated HTML after: /path/to/tmp/ec2af394-984d-4bac-b9fb-92b4461fda1b-after.html
 * Screenshot before: /path/to/tmp/ec2af394-984d-4bac-b9fb-92b4461fda1b-before-webkit.png
 * Screenshot after: /path/to/tmp/ec2af394-984d-4bac-b9fb-92b4461fda1b-after-webkit.png
 * Gif animation: /path/to/tmp/ec2af394-984d-4bac-b9fb-92b4461fda1bwebkit.gif
 * CSS diff: "/Applications/DiffMerge" "path/to/tmp/3ef804f6-9496-4020-8193-b13f3d0a3255-before.css" "/path/to/tmp/3ef804f6-9496-4020-8193-b13f3d0a3255-after.css"