VOID KEYWORD
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.
Syntax
The syntax of void can be
either of the following two:
<head>
<script
type="text/javascript">
<!--
void func()
javascript:void func()
OR
void(func())
javascript:void(func())
//-->
</script>
</head>
Example 1
The most common use of
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:
<html>
<head>
<script
type="text/javascript">
<!--
//-->
</script>
</head>
<body>
<p>Click the following, This won't
react at all...</p>
<a href="javascript:void(document.write(“Hello
: 0”))">Click me!</a>
</body>
</html>
Output
Click the following, This won't react at
all...
Example 2
Take a look at the
following 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.
<html>
<head>
<script
type="text/javascript">
<!--
//-->
</script>
</head>
<body>
<p>Click the following, This
won't react at all...</p> <a
href="javascript:void(0)">Click me!</a> </body>
</html>
Output
Click the following, This won't react at
all...
Example 3
Another use of void is to
purposely generate the undefined
value as follows.
<html>
<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>
<body>
<p>Click the following to see
the result:</p> <form>
<input type="button"
value="Click Me" onclick="getValue();" />
</body>
</html>
Output
Click the following button to see the result:
Click Me
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