JavaScript® 24-Hour Trainer

Chapter 43. Optimizing Your Code

The applications you use every day have more than likely been in development for many years. The code behind them has been refined to make them more efficient and responsive to the user than they were at first. When first written, code is rarely the best it could be — usually far from it.

There's an old adage that most professional developers follow: "Make it run, and then make it run well." When you first write an application, don't worry about optimizing your code. Another adage is "Premature optimization is the root of all evil." Worry about making your application work, and after it works, then start optimizing your code.

There are three major aspects of JavaScript optimization. They are:

• Refactoring code

• Optimizing DOM code

• Using event delegation

Let's start by looking at how to refactor your code.

REFACTORING CODE

It's been recounted many times, but it's worth repeating: The faster your code downloads, the faster your application feels to the user. You don't have control over your users' connection speed, but you do have control over how big your code files are. The size of your code files depends on a variety of factors, but two things that often add to code size are code duplication and unnecessary statements.

Refactoring Duplicate Code

You can cut the size of your code by refactoring duplicated code. When you refactor your code, you improve it without changing its external behavior. The most common means of refactoring code is identifying duplicated ...