W3cubDocs

/JavaScript

return

The return ends function execution and specifies a value to be returned to the function caller.

Syntax

return [expression]; 
expression
The expression whose value is to be returned. If omitted, undefined is returned instead.

Description

When a return statement is used in a function body, the execution of the function is stopped. If specified, a given value is returned to the function caller. For example, the following function returns the square of its argument, x, where x is a number.

function square(x) {
   return x * x;
}
var demo = square(3);
// demo will equal 9

If the value is omitted, undefined is returned instead.

The following return statements all break the function execution:

return;
return true;
return false;
return x;
return x + y / 3;

Automatic Semicolon Insertion

The return statement is affected by automatic semicolon insertion (ASI). No line terminator is allowed between the return keyword and the expression.

return
a + b;

is transformed by ASI into:

return; 
a + b;

The console will warn "unreachable code after return statement".

Starting with Firefox 40, a warning is shown in the console if unreachable code is found after a return statement.

To avoid this problem (to prevent ASI), you could use parentheses:

return (
  a + b
);

Examples

Interrupt a function

A function immediately stops at the point where return is called.

function counter() {
  for (var count = 1; ; count++) {  // infinite loop
    console.log(count + 'A'); // until 5
      if (count === 5) {          
        return;
      }
      console.log(count + 'B');  // until 4
    }
  console.log(count + 'C');  // never appears
}

counter();

// Output:
// 1A
// 1B
// 2A
// 2B
// 3A
// 3B
// 4A
// 4B
// 5A

Returning a function

See also the article about Closures.

function magic() {
  return function calc(x) { return x * 42; };
}

var answer = magic();
answer(1337); // 56154

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
return 1 12 1 3 3 1
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
return 1 18 4 10.1 1 1.0
Server
Node.js
return 0.1.100

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/return