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• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

size accessor property returns the number of elements in a Map 对象。

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.

描述

值 size is an integer representing how many entries the Map object has. A set accessor function for size is undefined ; you can not change this property.

范例

使用 size

var myMap = new Map();
myMap.set('a', 'alpha');
myMap.set('b', 'beta');
myMap.set('g', 'gamma');
myMap.size // 3
					

规范

规范
ECMAScript (ECMA-262) The definition of 'Map.prototype.size' 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
size	Chrome 38	Edge 12	Firefox 19 19 From Firefox 13 to Firefox 18, the size property was implemented as a Map.prototype.size() method, this has been changed to a property in later versions conform to the ECMAScript 2015 specification.	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 19 19 From Firefox 13 to Firefox 18, the size property was implemented as a Map.prototype.size() method, this has been changed to a property in later versions conform to the ECMAScript 2015 specification.	Opera Android 25	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12

图例

完整支持

完整支持

见实现注意事项。

另请参阅

• Map

元数据

• 最后修改： Jan 15, 2020

相关话题

1. 标准内置对象
2. Map
3. 特性
   1. Map.prototype.size
   2. Map.prototype[@@toStringTag]
   3. get Map[@@species]
4. 方法
   1. Map.prototype.clear()
   2. Map.prototype.delete()
   3. Map.prototype.entries()
   4. Map.prototype.forEach()
   5. Map.prototype.get()
   6. Map.prototype.has()
   7. Map.prototype.keys()
   8. Map.prototype.set()
   9. Map.prototype.values()
   10. Map.prototype[@@iterator]()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 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()