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    The function keyword can be used to define a function inside an expression.


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


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


    A function expression is very similar to and has almost the same syntax as a function statement (see function statement for details). The main difference between a function expression and a function statement is the function name, which can be omitted in function expressions to create anonymous functions. See also the chapter about functions for more information.


    The following example defines an unnamed function and assigns it to x. The function returns the square of its argument:

    var x = function(y) {
       return y * y;

    Named function expression

    If you want to refer to the current function inside the function body, you need to create a named function expression. This name is then local only to the function body (scope). This also avoids using the non-standard arguments.callee property.

    var math = {
      'factorial': function factorial(n) {
        if (n <= 1)
          return 1;
        return n * factorial(n - 1);


    Specification Status Comment
    ECMAScript 3rd Edition. Standard Initial definition. Implemented in JavaScript 1.5
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Function definition' in that specification.
    ECMAScript 6 (ECMA-262)
    The definition of 'Function definitions' in that specification.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Contributors to this page: Sevenspade
    Last updated by: Sevenspade,
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