There’s been two really interesting videos released recently that use the “Local Overrides” feature of Chrome DevTools in order to play with web performance without even touching the original source code.
From Johnny’s dev blog:
The challenge: Calculate the real percentage of unused CSS
Our goal is to create a script that will measure the percentage of unused CSS of this page. Notice that the user can interact with the page
Triggering a debugger; statement at just the right moment can help you select a DOM element that is really hard (or impossible) to get selected in DevTools. You can do that directly in your code, or, through a setTimeout right in the console, so you can get the DOM just how you want it right before it's frozen.