Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

6.13 var

The var



statement allows you to explicitly
declare a variable or variables. The syntax of this statement is:

var name_1 [ = value_1] [ ,..., name_n [= value_n]]

The var keyword is followed by a comma-separated
list of variables to declare; each variable in the list may
optionally have an initializer expression that specifies its initial
value. For example:

var i;
var j = 0;
var p, q;
var greeting = "hello" + name;
var x = 2.34, y = Math.cos(0.75), r, theta;

The var statement defines each named variable by
creating a property with that name either in the call object of the
enclosing function or, if the declaration does not appear within a
function body, in the global object. The property or properties
created by a var statement cannot be deleted with
the delete operator. Note that enclosing a
var statement in a with
statement (see Section 6.18)
does not change its behavior.

If no initial value is specified for a variable with the
var statement, the variable is defined but its
initial value is undefined.

Note that the var statement can also appear as
part of the for
and for/in loops. For
example:

for(var i = 0; i < 10; i++) document.write(i, "<br>");
for(var i = 0, j=10; i < 10; i++,j--) document.write(i*j, "<br>");
for(var i in o) document.write(i, "<br>"); 

Chapter 4 contains much more information on
JavaScript variables and variable declarations.