The
void is an important keyword in JavaScript which can be
used as a unary operator that appears before its single operand, which
may be of any type.
This operator specifies an expression to be evaluated without returning a value. Its syntax could be one of the following:
<head>
<script type="text/javascript">
<!--
void func()
javascript:void func()
or:
void(func())
javascript:void(func())
//-->
</script>
</head>
|
Example 1:
The most common use for this operator is in a client-side
javascript: URL, where it allows you to evaluate an expression
for its side effects without the browser displaying the value of the evaluated expression.
Here the expression
alert('Warning!!!') is evaluated but it is not loaded back into the current document:
<head>
<script type="text/javascript">
<!--
//-->
</script>
</head>
<body>
<a href="javascript:void(alert('Warning!!!'))">Click me!</a>
</body>
|
Example 2:
Another example the following link does nothing because the
expression "0" has no effect in JavaScript. Here the expression "0" is
evaluated but it is not loaded back into the current document:
<head>
<script type="text/javascript">
<!--
//-->
</script>
</head>
<body>
<a href="javascript:void(0))">Click me!</a>
</body>
|
Example 3:
Another use for
void is to purposely generate the
undefined value as follows:
<head>
<script type="text/javascript">
<!--
function getValue(){
var a,b,c;
a = void ( b = 5, c = 7 );
document.write('a = ' + a + ' b = ' + b +' c = ' + c );
}
//-->
</script>
</head>
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