JavaScript Cookbook

Chapter 10. Debugging and Error Handling

10.0. Introduction

It would be wonderful if we could, by some miracle, manage to create JavaScript applications that never fail, never have errors, never go wrong. Then we would have perfection and wouldn’t need things like debuggers and error handling. But what would be the fun in that?

There are two types of errors in JavaScript. The first is a programming error, where we, the JavaScript developers, do something wrong. These types of errors are typically found using our favorite browser and our favorite debugger.

At a minimum, what we need from a debugger is the ability to stop program execution and then examine variables and objects at that point. It also helps if we can continue the program by steps, drill into functions, and examine network activity and the state of the DOM at any time. However, we can usually manage debugging if we have the ability to stop a program and examine object values.

The second type of error occurs when the web page reader answers a question incorrectly, pushes the wrong button, or tries to type in a Social Security number when we’re expecting a name. Or the error can happen when we’re mixing libraries and something goes wrong between them. We’ll look at these kinds of errors first, and then we’ll get into the various browsers and their debugging capabilities.

10.1. Gracefully Handling No JavaScript Support

Problem

You want to ensure your pages work as well with JavaScript turned off as when it’s turned on.

Solution ...