For anyone looking to test overriding an existing js file:

• Open dev tools in Chrome
• Go to the Sources tab
• Press ctrl + p to search for your JavaScript file
• Find the file by typing the name, then press enter
• Right click the tab it opened and click "Reveal in navigator sidebar"
• Right click the file in the sidebar and click "Override content"
• Make edits in the open file in Chrome and ctrl + s to save, then reload

I realize this is not the exact nature of the question here, but this is the post I found when looking for how to override a js file in Chrome, so maybe it'll help someone else.