From the Duckett HTML book

Chapter - 10 Error Handling & Debugging

Debugging is the process of finding errors. It involves a process of deduction.The console helps narrow down the area in which the error is located, so you can try to find the exact error. JavaScript has 7 different types of errors.Each creates its own error object, which can tell you its line number and gives a description of the error. If you know that you may get an error, you can handle it gracefully using the try, catch, finally statements. Use them to give your users helpful feedback. If you understand execution contexts (which have two stages) and stacks, you are more likely to find the error in your code.