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rated 0 times [  57] [ 1]  / answers: 1 / hits: 28725  / 15 Years ago, fri, march 20, 2009, 12:00:00

I've seen some people using void operator in their code. I have also seen this in href attributes: javascript:void(0) which doesn't seem any better than javascript:;

So, what is the justification of using the void operator?

More From » void


The JavaScript, the void operator is used to explicitly return undefined. It's a unary operator, meaning only one operand can be used with it. You can use it like shown below — standalone or with a parenthesis.

void expression;

Lets see some examples:

void 0; //returns undefined
void(1); //returns undefined

void 'hello'; //undefined
void {}; //undefined
void []; //undefined

void myFunction();

If you ask why do you need a special keyword just to return undefined instead of just returning undefined: the reason is that before ES5 you could actually name a global variable undefined, like so: var undefined = "hello" or var undefined = 23, and most browsers would accept it; the identifier undefined was not promised to actually be undefined¹. So, to return the actual undefined value, the void operator is/was used. It's not a very popular operator though and is seldom used.

Let's see an example of function with void:

//just a normal function
function test() {
return 2;

//lets call it
console.log(test()); //output is hello followed by 2

//now lets try with void
console.log(void test()); //output is hello followed by undefined

void discards the return value from the function and explicitly returns undefined.

You can read more from my tutorial post:

¹ In ECMAScript 5 and later, the global variable undefined is guaranteed to be undefined (ECMA-262 5th Ed., §, though it is still possible to have a variable inside an inner scope be named undefined.

[#99816] Sunday, March 15, 2009, 15 Years  [reply] [flag answer]
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