The error console is a utility built in to your browser that shows error messages whenever a script error is encountered.

Constant use of the error console is essential in tracking-down errors in scripts, particularly during development.

Failure to use the error console during development/debugging will cause unnecessary frustration and lost time.

If you are being taught Javascript as a student and you didn't know about the error console, ask your teacher why he/she failed to teach you to use it at the appropriate time, which was during your first lecture immediately after the class typed-in their first test script. If your teacher disgrees with that assertion, please send them to the forum that issued this link.

At the time of writing, the browser with the most useful built-in error console is Mozilla FireFox. It is accessed via the Tools menu. In addition there is a Firefox debugger plugin available called Firebug .