HTML and CSS Reference
In-Depth Information
<script type=”text/javascript”>
var message = “My message”;
In that example, I created a variable called message and then passed its value as an argu-
ment to document.write() . You can also assign the results of an expression to a vari-
var sum = 5 + 5;
And you can use variables in your expressions:
var firstName = “George”;
var lastName = “Washington”;
var name = firstName + “ “ + lastName;
Let's break down a variable declaration into pieces. Here's a declaration:
var message = “My message”;
The line begins with var , which indicates that this is a variable declaration. The name of
this variable is message . There are a number of rules that apply to naming variables. I list
them shortly. The assignment operator (=) is used to assign a value to the variable when
it's declared. The value on the right side of the operator is assigned to the newly declared
Variable names must conform to the following rules:
Variable names can include only letters, numbers, and the underscore (_) or dollar
sign ($) character.
Variable names cannot start with a number.
You cannot use any reserved words as a variable name. Reserved words are words
that have a specific meaning for the JavaScript interpreter. For example, naming a
variable named var won't work. Table 14.2 contains a full list of JavaScript
reserved words.
As a matter of style, JavaScript variables begin with a lowercase letter. If a variable
name contains multiple words, usually an underscore is used to join the two
words, or the first letter of the second word is uppercase. So you would write
my_variable or myVariable .
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