在此页

• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

length property indicates the number of parameters expected by the function.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

特性属性在 Function.length
可写	no
可枚举	no
可配置	yes

描述

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 其余参数 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

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.

范例

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
					

规范

规范
ECMAScript (ECMA-262) The definition of 'Function.length' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
length	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs Yes
Configurable: true	Chrome 43	Edge 12	Firefox 37	IE No	Opera 30	Safari No	WebView Android 43	Chrome Android 43	Firefox Android 37	Opera Android 30	Safari iOS No	Samsung Internet Android 4.0	nodejs Yes

图例

完整支持

完整支持

不支持

不支持

另请参阅

• Function

元数据

• 最后修改： May 7, 2020

相关话题

1. 标准内置对象
2. Function
3. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
4. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
5. 继承：
6. Object
7. 特性
   1. Object.prototype.__proto__
   2. Object.prototype.constructor
8. 方法
   1. Object.prototype.__defineGetter__()
   2. Object.prototype.__defineSetter__()
   3. Object.prototype.__lookupGetter__()
   4. Object.prototype.__lookupSetter__()
   5. Object.prototype.hasOwnProperty()
   6. Object.prototype.isPrototypeOf()
   7. Object.prototype.propertyIsEnumerable()
   8. Object.prototype.toLocaleString()
   9. Object.prototype.toSource()
   10. Object.prototype.toString()
   11. Object.prototype.valueOf()
   12. Object.setPrototypeOf()