Function.length

Summary

The length property specifies the number of arguments expected by the function.

Description

length is a property of a function object, and indicates how many arguments the function expects, i.e. the number of formal parameters. This number does not include the rest parameter. By contrast, arguments.length is local to a function and provides the number of arguments actually passed to the function.

Data property of the Function constructor

The Function constructor is itself a Function object. It's length data property has a value of 1. The property attributes are: Writable: false, Enumerable: false, Configurable: true.

Property of the Function prototype object

The length property of the Function prototype object has a value of 0.

Examples

console.log ( Function.length ); /* 1 */

console.log( (function ()        {}).length ); /* 0 */
console.log( (function (a)       {}).length ); /* 1 */
console.log( (function (a, b)    {}).length ); /* 2 etc. */
console.log( (function (...args) {}).length ); /* 0, rest parameter is not counted */

Specifications

Browser compatibility

See also

• Function