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Chris Bongers
Chris Bongers

Posted on • Originally published at

Chrome find unused code 🔎

Nowadays, we have PurgeCSS, which is cool at identifying what CSS is being used and not.
But did you know Chrome also has the option to show you what CSS and JavaScript are actually being used, and what not?

Yes, Chrome has a Code Coverage tool!

Finding the Chrome coverage tool

We can access this tool by opening up the development tools.

Mac Cmd + Shift + C or Windows: Ctrl + Shift + C.

Next click the three dots -> More tools -> Coverage.

Chrome coverage window

This will open up a coverage window.

Running a coverage

To run a coverage, we can simply press the reload button in the coverage window.

By doing this, Chrome will re-index the page and show you all the results it found like this.

Chrome coverage report

This is the high-level overview of the scripts and css loaded on the page. But how can we now see what's being used or not?

Click on one of the results to see it in detail.

Chrome coverage CSS result

Here you see my inline CSS. Depending on the colour you can see if a line is being used or not.

In the above example, the red lines are not being used.

Do be aware when removing the CSS. It might be used on another page!

So this is really cool, it will give you at least a starting ground if you really want to optimise it to the next level!

It also works for JavaScript, but keep in mind this JavaScript just might not have been fired yet.

Code coverage JavaScript

Exporting this data

There is also the option to export these results from the coverage.
You could use another tool to then automated remove these lines from your code.

You can find the export in the coverage window.

Chrome coverage export

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