Debug Script In Browser's Devtools

1. You can do that by adding the "debugger;" keyword anywhere in your widget or dashboard script, opening the developer console and refreshing. As the script is processed by the browser, it will stop execution at this point in the script and behave just like a manually added breakpoint.

2. It should work in all plugins without issue. First of all, try placing a "console.log" at the exact location of your "debugger" statement and see if that does work - that is, if that line is really reached. 

Additionally, with plugins you can use Chrome's DevTools to place breakpoints anywhere in your code. You can find the plugin code in the location outlined in this screenshot below - find the code you're interested in, place a breakpoint and reload to see if that does stop.