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Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

Obsolete since Gecko 60 (Firefox 60 / Thunderbird 60 / SeaMonkey 2.57)
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

Non-standard. Do not use!
The expression closure syntax is a deprecated Firefox-specific feature and has been removed starting with Firefox 60. For future-facing usages, consider using arrow functions.

Expression closures are a shorthand function syntax for writing simple functions.

Syntax

function [name]([param1[, param2[, ..., paramN]]])
   expression

Parameters

name
The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.
paramN
The name of an argument to be passed to the function. A function can have up to 255 arguments.
expression
The expression which comprise the body of the function.

Description

This addition is nothing more than a shorthand for writing simple functions, giving the language something similar to a typical Lambda notation.

JavaScript 1.7 and older:

function(x) { return x * x; }

JavaScript 1.8:

function(x) x * x

This syntax allows you to leave off the braces and 'return' statement - making them implicit. There is no added benefit to writing code in this manner, other than having it be syntactically shorter.

Examples

A shorthand for binding event listeners:

 document.addEventListener('click', function() false, true);

Using this notation with some of the array functions from JavaScript 1.6:

elems.some(function(elem) elem.type == 'text');

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Basic support
DeprecatedNon-standard
Chrome No support NoEdge No support NoFirefox No support 3 — 60IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile No support NoFirefox Android No support 4 — 60Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support Nonodejs No support No

Legend

No support  
No support
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.

See also

Document Tags and Contributors

Contributors to this page: ExE-Boss, fscholz, nmve, arai
Last updated by: ExE-Boss,