JavaScript Programming: Debugging

by Heidi Brumbaugh

Learning JavaScript can be liberating, even fun. Scripting gives you the power to make your pages more dynamic and interesting. Best of all, its flexibility lets you add your own touches to personalize your page. If you've been following along in this series and--I hope--experimenting and testing out your own ideas about what might or might not work, you have more than likely already encountered your first error message.

You know what I'm talking about. You plan the perfect script for hours, check and double-check the documentation, enter the code in carefully bracketed <SCRIPT> tags, recheck your brilliant logic, save out the HTML file and load it into your browser, prepare to be dazzled, and...your ungrateful browser comes back:

Netscape - (Alert) JavaScript Error: script.html ,
line 40
syntax error
else
. . . . . . . . . . . ^

If you've programmed in C, Basic, or another scripting language, you're likely to sigh and dig in. Here we go again. If you're new to programming, however, these error messages can be frustrating and discouraging. This article gives you an overview of the debugging process and some tips that will serve you well here, as well as elsewhere in your programming life.

What is a Bug?

A bug is an instruction in a program that is causing an undesirable result. There are two main types of bugs: Syntax and logic errors. Syntax errors happen when you say something the computer doesn't understand, causing program interpretation to stop. Logic errors are when the program works, but doesn't do what you thought you meant.

[Move on the Part II]

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