Debug compiled CSS and JS in Firefox using sourcemaps

If you haven’t used sourcemaps, now is the time!

With the advent of compiled CSS like LESS or SASS, or minified/uglified JS, it makes debugging awkward as you cant see the original lines of code that you wrote. Cue CTRL_F’ing to find that line to tweak! But not any more!

When you generate your LESS/SASS, if you tell it to compile a sourcemap too, it will create one! This allows your browser to report which line of the less or scss file the rule in question came from.

For the Less compiler command, you have several options:

--source-map[=FILENAME]  Outputs a v3 sourcemap to the filename (or output filename.map)
--source-map-rootpath=X  adds this path onto the sourcemap filename and less file paths
--source-map-basepath=X  Sets sourcemap base path, defaults to current working directory.
--source-map-less-inline puts the less files into the map instead of referencing them
--source-map-map-inline  puts the map (and any less files) into the output css file
--source-map-url=URL     the complete url and filename put in the less file

For Sass, you just add the option at the end of the command:

sass sass/screen.scss:stylesheets/screen.css --sourcemap

Now in Firefox, open your page, right click, and click Inspect Element (not the Firebug one, the default Firefox Inspector!)

In the CSS rules pane, right click, and make sure show original sources is checked.

To the right of the actual rule, you click the link which would usually take you to the CSS file for viewing, but now, it takes you to your Less/Sass file! You can now tweak rules and save them directly from the inspector!

In my new workplace, our SASS files are compiled by Gulp automatically. (In my last work I had lessc configured in PHPStorm). If your own files are automatically built, then you should also checkout Firefox addons for live reloading! The great thing about that is that the CSS files update without refreshing! Great if you have session info or other info that might need reinstantiating, you dont have to keep keying stuff in! Have fun!

Using file watchers with PHPStorm

I love LESS! However having to run lessc every time I edit my less file is LAME! Adding File watchers in PHPStorm means that when you save your file, it will automatically compile your CSS! We are also going to add Javascript and CSS minification, which helps increase page load speeds and also make it harder for nosey people to examine your javascript! Lets go!

First up, lets install node.js by visiting http://nodejs.org/
Next, we install less and yuicompressor:

npm install -g less
 npm install -g yuicompressor

Also on Windows, everything cracks up unless you add a PATH environment variable for the modules. In Control Panel in System, click Advanced System Settings, click Environment Variables and add the node modules folder to the PATH variable, or add it if its not there:

C:\Users\your.username\AppData\Roaming\npm

Go to File > Settings, and under the project settings look for File Watchers. Click the green + to add a watcher. Select LESS.

All that is required is that you put the correct path into the program field. This may be slightly different depending on your setup. For windows users, the modules can usually be found in :

C:\Users\your.username\AppData\Roaming\npm\lessc.cmd
 C:\Users\your.username\AppData\Roaming\npm\yuicompressor.cmd

And on linux machines, you can find it elsewhere. I cant remember offhand, but just take note of the output while you are installing it and you wont go far wrong.

Now you can edit the head section of your website, replacing style.css with style.min.css, and the same also for your javascript! Awesome 🙂