javascript

Chapter 20: Best Practices
};
//set a timeout - fixed
setTimeout(function(){
alert(‘Hello world!’);
}, 500);
To increase the performance of your code, avoid using strings that need to be interpreted as JavaScript
whenever possible.
Other Performance Considerations
There are a few other things to consider when evaluating the performance of your script. The following
aren ’ t major issues, but they can make a difference when used frequently:
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Native methods are fast — Whenever possible, use a native method instead of one written in
JavaScript. Native methods are written in compiled languages such as C or C++ and thus run
much faster than those in JavaScript. The most often forgotten methods in JavaScript are the
complex mathematical operations available on the Math object; these methods always run faster
than any JavaScript equivalent for calculating sine, cosine, and so on.
Switch statements are fast — If you have a complex series of if - else statements, converting it
to a single switch statement can result in faster code. You can further improve the performance
of switch statements by organizing the cases in the order of most likely to least likely.
Bitwise operators are fast — When performing mathematical operations, bitwise operations are
always faster than any Boolean or numeric arithmetic. Selectively replacing arithmetic
operations with bitwise operations can greatly improve the performance of complex
calculations. Operations such as modulus, logical AND, and logical OR are good candidates to
be replaced with bitwise operations.
Minimize Statement Count
The number of statements in JavaScript code affects the speed with which the operations are performed.
A single statement can complete multiple operations faster than multiple statements each performing a
single operation. The task, then, is to seek out statements that can be combined, in order to decrease the
execution time of the overall script. To do so, there are several patterns to look for.
Multiple Variable Declarations
One area in which developers tend to create too many statements is in the declaration of multiple
variables. It ’ s quite common to see code declaring multiple variables using multiple var statements,
such as the following:
//four statements - wasteful
var count = 5;
var color = “blue”;
var values = [1,2,3];
var now = new Date();
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