The void operator

JavaScriptJunior~1 min read

The void operator in JavaScript is a fairly rare but important tool. It is used to evaluate an expression without returning a value, meaning it always returns undefined, regardless of what the expression does.

Syntax

javascript

void expression

javascript

void(expression)

Main idea

The void operator evaluates the expression, but always returns undefined.

Example

javascript

void 123;       // undefined
void 'hello';   // undefined
void (5 + 5);   // undefined

It doesn't matter what the expression on the right evaluates to, the result of void is always undefined.

Example with a function

javascript

function sayHi() {
  console.log('Hello!');
  return 'Hi';
}

console.log(sayHi());   // "Hi"
console.log(void sayHi()); // runs, but returns undefined

Here, sayHi() is called, but the result ('Hi') is ignored, and undefined is returned.

Where it's used in practice

Sometimes you need a link click to do nothing:

javascript

<a href="javascript:void(0)">Click me</a>

Here:

void(0) is executed → undefined

the browser doesn't navigate anywhere, because href doesn't provide a URL.

This is a legacy practice; in modern code it's better to use href="#" with event.preventDefault().

For IIFEs (immediately invoked function expressions)

void used to be used to guarantee correct execution of an IIFE:

javascript

void function() {
  console.log('It worked!');
}();

Without void, the parser could confuse the expression with a function declaration. This need is rare nowadays, but historically void was used as a "safety net".

In arrow functions, to "return nothing"

javascript

const log = msg => void console.log(msg);

log('Hello'); // logs to the console, but returns undefined

Here, void is used to perform an action without returning a value.

In bookmarklets (mini-scripts in bookmarks)

An example of a "bookmarklet":

javascript

javascript:void(alert('Hello'))

Without void, the browser would try to navigate to a "page" with the expression's result (e.g., undefined), and void prevents that.

Example: comparison with a regular call

javascript

function calc() {
  return 42;
}

console.log(calc());      // 42
console.log(void calc()); // undefined

The function runs, but void forces the expression to return undefined.

Summary

What it does	Evaluates an expression and returns `undefined`
Returns	`undefined`
Used for	Ignoring the expression's result
Common scenarios	`javascript:void(0)` links, IIFEs, arrow functions without a return

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