1. In the Sources tab, open the .js file from the Page panel in the left sidebar. Set a breakpoint by clicking on the line number.
2. Perform the action necessary to trigger that line of code, which will pause the execution at the breakpoint.
3. Use the toolbar on the right sidebar to step-in/step-out, watch expressions, local vars while debugging through the code.
4. Alternatively, you can also add the debugger; statement in the code to pause execution of the code at that line.

[1] "Use Debugger pane", by Edge DevTools Docs