The length
property indicates the number of parameters expected by the function.
Function.length
Try it
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
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 are counted
Specifications
Browser compatibility
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
length |
1
|
12
|
1
|
4
|
3
|
1
|
1
|
18
|
4
|
10.1
|
1
|
1.0
|
1.0
|
0.10.0
|
configurable_true |
43
|
12
|
37
|
No
|
30
|
10
|
43
|
43
|
37
|
30
|
10
|
4.0
|
1.0
|
4.0.0
|
See also
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length