Add the debugger statement in your content script
var foo = 1; debugger; foo = 2;
Open the Developer Tool on the web page where your content script is injected to see the code execution pause at those lines.
Tip: To reload the extension, you can press F5 inside the developer tools window. You can put breakpoints in the initialization code before reloading.
Tip: Right-clicking the extension action button and selecting "Manage extensions" will open
chrome://extensions page scrolled to that extension.
You have 2 ways to debug the popup window. Both ways are by using the Chrome DevTools.
Option 1: Right click the extension's action button, and choose Inspect popup
Option 2: Open the popup window, directly in your browser as a tab.
For example, if you extension id is
abcdefghijkmnop, and your popup html file is
popup.html. Go to the address and navigate to:
Now you see the poup in regular tab. And you can press F12 to open the developer tools.