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JavaScript - Void Keyword

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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>

To understand it in better way you can Try it yourself.

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>

To understand it in better way you can Try it yourself.

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>

To understand it in better way you can Try it yourself.


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