What Does "JavaScript:Void(0)" Mean

What does javascript:void(0) mean?

The void operator evaluates the given
expression and then returns undefined.

The void operator is often used merely
to obtain the undefined primitive
value, usually using “void(0)” (which
is equivalent to “void 0”). In these
cases, the global variable undefined
can be used instead (assuming it has
not been assigned to a non-default
value).

An explanation is provided here: void operator.

The reason you’d want to do this with the href of a link is that normally, a javascript: URL will redirect the browser to a plain text version of the result of evaluating that JavaScript. But if the result is undefined, then the browser stays on the same page. void(0) is just a short and simple script that evaluates to undefined.

What does `void 0` mean?

What does void 0 mean?

void^[MDN] is a prefix keyword that takes one argument and always returns undefined.

Examples

void 0
void (0)
void "hello"
void (new Date())
//all will return undefined

What's the point of that?

It seems pretty useless, doesn't it? If it always returns undefined, what's wrong with just using undefined itself?

In a perfect world we would be able to safely just use undefined: it's much simpler and easier to understand than void 0. But in case you've never noticed before, this isn't a perfect world, especially when it comes to Javascript.

The problem with using undefined was that undefined is not a reserved word (it is actually a property of the global object ^[wtfjs]). That is, undefined is a permissible variable name, so you could assign a new value to it at your own caprice.

alert(undefined); //alerts "undefined"
var undefined = "new value";
alert(undefined) // alerts "new value"

Note: This is no longer a problem in any environment that supports ECMAScript 5 or newer (i.e. in practice everywhere but IE 8), which defines the undefined property of the global object as read-only (so it is only possible to shadow the variable in your own local scope). However, this information is still useful for backwards-compatibility purposes.

alert(window.hasOwnProperty('undefined')); // alerts "true"
alert(window.undefined); // alerts "undefined"
alert(undefined === window.undefined); // alerts "true"
var undefined = "new value";
alert(undefined); // alerts "new value"
alert(undefined === window.undefined); // alerts "false"

void, on the other hand, cannot be overidden. void 0 will always return undefined. undefined, on the other hand, can be whatever Mr. Javascript decides he wants it to be.

Why void 0, specifically?

Why should we use void 0? What's so special about 0? Couldn't we just as easily use 1, or 42, or 1000000 or "Hello, world!"?

And the answer is, yes, we could, and it would work just as well. The only benefit of passing in 0 instead of some other argument is that 0 is short and idiomatic.

Why is this still relevant?

Although undefined can generally be trusted in modern JavaScript environments, there is one trivial advantage of void 0: it's shorter. The difference is not enough to worry about when writing code but it can add up enough over large code bases that most code minifiers replace undefined with void 0 to reduce the number of bytes sent to the browser.

href= javascript: vs. href= javascript:void(0)

It does not cause problems but it's a trick to do the same as PreventDefault

when you're way down in the page and an anchor as:

<a href="#" onclick="fn()">click here</a>

you will jump to the top and the URL will have the anchor # as well, to avoid this we simply return false; or use javascript:void(0);

regarding your examples

<a onclick="fn()">Does not appear as a link, because there's no href</a>

just do a {text-decoration:underline;} and you will have "link a-like"

<a href="javascript:void(0)" onclick="fn()">fn is called</a>
<a href="javascript:" onclick="fn()">fn is called too!</a>

it's ok, but in your function at the end, just return false; to prevent the default behavior, you don't need to do anything more.

Why use javascript:void(0) instead of # in href?

<a href="#">link</a>

adds # to the browser url and jumps to the top of the page.

<a href="javascript:void(0);">link</a>

simply "ignores" the link click.

<a href="#" onclick="return false;">link</a>

also ignores the href.

Don't forget that in some cases javascript might be disabled (very uncommon).

why we are using javascript:void(0) in Angular code

javascript:void(0)

The snippet show above simply ignores the link "click." This can be done in a similar fashion by the following:

<a href="#" onclick="return false;">link</a>

---

Related Topics