The length
property indicates the number of parameters expected by the function.
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Property attributes of Function.length |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | yes |
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 excludes the rest parameter and only includes parameters before the first one with a default value. 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. Its 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
Using function length
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 console.log((function(a, b = 1, c) {}).length); // 1, only parameters before the first one with // a default value is counted
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Function.length' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
length | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support 3 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Configurable: true | Chrome Full support 43 | Edge Full support 12 | Firefox Full support 37 | IE No support No | Opera Full support 30 | Safari No support No | WebView Android Full support 43 | Chrome Android Full support 43 | Firefox Android Full support 37 | Opera Android Full support 30 | Safari iOS No support No | Samsung Internet Android Full support 4.0 | nodejs Full support Yes |
Legend
- Full support
- Full support
- No support
- No support