void

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

Syntax

void expression

Description

This operator allows inserting expressions that produce side effects into places where an expression that evaluates to undefined is desired.

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).

Immediately Invoked Function Expressions

When using an immediately-invoked function expression, void can be used to force the function keyword to be treated as an expression instead of a declaration.

void function iife() {
    var bar = function () {};
    var baz = function () {};
    var foo = function () {
        bar();
        baz();
     };
    var biz = function () {};

    foo();
    biz();
}();

JavaScript URIs

When a browser follows a javascript: URI, it evaluates the code in the URI and then replaces the contents of the page with the returned value, unless the returned value is undefined. The void operator can be used to return undefined. For example:

<a href="javascript:void(0);">
  Click here to do nothing
</a>

<a href="javascript:void(document.body.style.backgroundColor='green');">
  Click here for green background
</a>

Note, however, that the javascript: pseudo protocol is discouraged over other alternatives, such as unobtrusive event handlers.

Specifications

Specification	Status	Comment
ECMAScript 2017 Draft (ECMA-262) The definition of 'The void Operator' in that specification.	Draft
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'The void Operator' in that specification.	Standard
ECMAScript 5.1 (ECMA-262) The definition of 'The void Operator' in that specification.	Standard
ECMAScript 3rd Edition (ECMA-262) The definition of 'The void Operator' in that specification.	Standard
ECMAScript 1st Edition (ECMA-262) The definition of 'The void Operator' in that specification.	Standard	Initial definition. Implemented in JavaScript 1.1

Browser compatibility

See also

• undefined