↑
Main Page

variables in ECMAScript

The previous code defines the variable

test

to have a value of

“hi”

and the variable

test2

to have a

value of

“hola”

. Variables using the same

var

statement don’t have to be of the same type, however, as

shown in the following:

var test = “hi”, age = 25;

This example defines

test

(yet again) in addition to another variable named

age

that is set to the value

. Even though

test

and

age

are two different data types, this is perfectly legal in ECMAScript.

Unlike Java, variables in ECMAScript do not require initialization (they are actually initialized behind

the scenes, which I discuss later). Therefore, this line of code is valid:

var test;

Also unlike Java, variables can hold different types of values at different times; this is the advantage of

loosely typed variables. A variable can be initialized with a string value, for instance, and later on be set

to a number value, like this:

var test = “hi”;

alert(test); //outputs “hi”

//do something else here

test = 55;

alert(test); //outputs “55”

This code outputs both the string and the number values without incident (or error). As mentioned pre-

viously, it is best coding practice for a variable to always contain a value of the same type throughout

its use.

In terms of variables names, a name must follow two simple rules:

The first character must be a letter, an underscore (

), or a dollar sign (

All remaining characters may be underscores, dollar signs, or any alphanumeric characters.

All the following variable names are legal:

var test;

var $test;

var $1;

var _$te$t2;

Of course, just because variable names are syntactically correct doesn’t mean you should use them.

Variables should adhere to one of the well-known naming conventions:

Camel Notation — the first letter is lowercase and each appended word begins with an upper-

case letter. For example:

var

est

alue = 0,

econd

est

alue = “hi”;

ECMAScript Basics

05_579088 ch02.qxd 3/28/05 11:35 AM Page 13