Expression closures

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

Gecko specific note

Starting with Gecko / SpiderMonkey 45 (Firefox 45 / Thunderbird 45 / SeaMonkey 2.42), console warnings are added when expression closures are used (bug 995610).

See also

• Functions and function scope
• Function
• function statement
• function expression
• function* statement
• function* expression
• GeneratorFunction