Debug JS code with chrome dev tool.

https://googlechrome.github.io/devtools-samples/debug-js/get-started

1. Click source tab
2. Select the source file in left panel tree
3. Create a break point in the line of source code editor
4. Show the console drawer in the right corner

Click the button on the web, manually apply code fix in console.

1. Resume code execution
2. Edit source code in code editor and ctrl+s
3. Deactivate the break point

Start verification on web page.