javascript

Chapter 20: Best Practices
Many JavaScript libraries now subscribe to this theory of development, allowing them to grow and
adapt even as browsers continually change.
Avoid Globals
Closely related to respecting object ownership is avoiding global variables and functions whenever
possible. Once again, this has to do with creating a consistent and maintainable environment in which
scripts will be executed. At most, a single global variable should be created on which other objects and
functions exist. Consider the following:
//two globals - AVOID!!!
var name = “Nicholas”;
function sayName(){
alert(name);
}
This code contains two globals: the variable name and the function sayName() . These can easily be
created on an object that contains both, as in this example:
//one global - preferred
var MyApplication = {
name: “Nicholas”,
sayName: function(){
alert(this.name);
}
};
This rewritten version of the code introduces a single global object, MyApplication , onto which both
name and sayName() are attached. Doing so clears up a couple of issues that existed in the previous
code. First, the variable name overwrites the window.name property, which possibly interferes with other
functionality. Second, it helps to clear up confusion over where the functionality lives. Calling
MyApplication.sayName() is a logical hint that any issues with the code can be identified by looking
at the code in which MyApplication is defined.
An extension of the single global approach is the concept of namespacing, popularized by the Yahoo!
User Interface (YUI) library. Namespacing involves creating an object to hold functionality. In the 2.x
version of YUI, there were several namespaces onto which functionality was attached. Here are some
examples:
❑
❑
❑
YAHOO.util.Dom — Methods for manipulating the DOM
YAHOO.util.Event — Methods for interacting with events
YAHOO.lang — Methods for helping with low - level language features
For YUI, the single global object YAHOO serves as a container onto which other objects are defined.
Whenever objects are used simply to group together functionality in this manner, they are called
namespaces . The entire YUI library is built on this concept, allowing it to coexist on the same page with
any other JavaScript library.
The important part of namespacing is to decide on a global object name that everyone agrees to use and
that is unique enough that others aren ’ t likely to use it as well. In most cases, this can be the name of the
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