In Google Chrome right-click an element (or anything on the page) and choose Inspect Element to access GC's developer tools.



You can apparently use Ctrl-Shift-I to do this as well, although I find pressing F12 works as well. You can also access these tools from the browser's settings button (the burger button) and More tools.

The pane that opens at the bottom-left shows you the HTML for the element you were pointing at. Significantly though, at the top of the right pane will be a bright red circle indicating how many Javascript errors there were.



Click the red circle (the error indicator) and another pane will open further down showing you your Javascript errors. This pane is the Console.



Click the page-link at the far right of an error message and you will be taken to the line of your script that generated the error.



If you build web pages you must become familiar with your browser's developer tools!