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• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

Symbol.isConcatSpreadable well-known symbol is used to configure if an object should be flattened to its array elements when using the Array.prototype.concat() 方法。

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

@@isConcatSpreadable symbol ( Symbol.isConcatSpreadable ) can be defined as an own or inherited property and its value is a boolean. It can control behavior for arrays and array-like objects:

• For array objects, the default behavior is to spread (flatten) elements. Symbol.isConcatSpreadable can avoid flattening in these cases.
• For array-like objects, the default behavior is no spreading or flattening. Symbol.isConcatSpreadable can force flattening in these cases.

特性属性在 Symbol.isConcatSpreadable
可写	no
可枚举	no
可配置	no

范例

Arrays

默认情况下， Array.prototype.concat() spreads (flattens) arrays into its result:

let alpha = ['a', 'b', 'c'],
let numeric = [1, 2, 3]
let alphaNumeric = alpha.concat(numeric)
console.log(alphaNumeric)  // Result: ['a', 'b', 'c', 1, 2, 3]
					

When setting Symbol.isConcatSpreadable to false , you can disable the default behavior:

let alpha = ['a', 'b', 'c'],
let numeric = [1, 2, 3]
numeric[Symbol.isConcatSpreadable] = false
let alphaNumeric = alpha.concat(numeric)
console.log(alphaNumeric)  // Result: ['a', 'b', 'c', [1, 2, 3] ]
					

Array-like objects

For array-like objects, the default is to not spread. Symbol.isConcatSpreadable needs to be set to true in order to get a flattened array:

let x = [1, 2, 3]
let fakeArray = {
  [Symbol.isConcatSpreadable]: true,
  length: 2,
  0: 'hello',
  1: 'world'
}
x.concat(fakeArray)  // [1, 2, 3, "hello", "world"]
					

注意： length property is used to control the number of object properties to be added. In the above example, length:2 indicates two properties has to be added.

规范

规范
ECMAScript (ECMA-262) The definition of 'Symbol.isconcatspreadable' 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
isConcatSpreadable	Chrome 48	Edge 15	Firefox 48	IE No	Opera 35	Safari 10	WebView Android 48	Chrome Android 48	Firefox Android 48	Opera Android 35	Safari iOS 10	Samsung Internet Android 5.0	nodejs 6.0.0

图例

完整支持

完整支持

不支持

不支持

另请参阅

• Array.prototype.concat()

元数据

• 最后修改： Jan 23, 2020

相关话题

1. 标准内置对象
2. Symbol
3. 特性
   1. Symbol.asyncIterator
   2. Symbol.hasInstance
   3. Symbol.isConcatSpreadable
   4. Symbol.iterator
   5. Symbol.match
   6. Symbol.matchAll
   7. Symbol.prototype.description
   8. Symbol.replace
   9. Symbol.search
   10. Symbol.species
   11. Symbol.split
   12. Symbol.toPrimitive
   13. Symbol.toStringTag
   14. Symbol.unscopables
4. 方法
   1. Symbol.for()
   2. Symbol.keyFor()
   3. Symbol.prototype.toSource()
   4. Symbol.prototype.toString()
   5. Symbol.prototype.valueOf()
   6. Symbol.prototype[@@toPrimitive]
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()