Symbol.isConcatSpreadable

内置的Symbol.isConcatSpreadable符号用于配置某对象作为Array.prototype.concat()方法的参数时是否展开其数组元素。

描述

@@isConcatSpreadable 符号 (Symbol.isConcatSpreadable) 可以直接定义为对象属性或继承而来,它是布尔类型。它可以控制数组或类似数组(array-like)的对象的行为:

  • 对于数组对象,默认情况下,用于concat时,会按数组元素展开然后进行连接(数组元素作为新数组的元素)。重置Symbol.isConcatSpreadable可以改变默认行为。
  • 对于类似数组的对象,用于concat时,该对象整体作为新数组的元素,重置Symbol.isConcatSpreadable可改变默认行为。
Symbol.isConcatSpreadable 属性的属性特性:
writable false
enumerable false
configurable false

示例

数组

默认情况下,Array.prototype.concat() 展开其元素连接到结果中:

var alpha = ['a', 'b', 'c'], 
    numeric = [1, 2, 3]; 

var alphaNumeric = alpha.concat(numeric); 

console.log(alphaNumeric); // 结果: ['a', 'b', 'c', 1, 2, 3]

设置Symbol.isConcatSpreadablefalse

var alpha = ['a', 'b', 'c'], 
    numeric = [1, 2, 3]; 

numeric[Symbol.isConcatSpreadable] = false;
var alphaNumeric = alpha.concat(numeric); 

console.log(alphaNumeric); // 结果: ['a', 'b', 'c', [1, 2, 3] ]

Array-like 对象

对于类数组 (array-like)对象,默认不展开。期望展开其元素用于连接,需要设置 Symbol.isConcatSpreadable 为true:

var x = [1, 2, 3];

var fakeArray = { 
  [Symbol.isConcatSpreadable]: true, 
  length: 2, 
  0: "hello", 
  1: "world" 
}

x.concat(fakeArray); // [1, 2, 3, "hello", "world"]

技术标准

标准 状态 备注
ECMAScript 2015 (6th Edition, ECMA-262)
Symbol.isconcatspreadable
Standard Initial definition.
ECMAScript (ECMA-262)
Symbol.isconcatspreadable
Living Standard No change.

浏览器兼容性

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
isConcatSpreadableChrome Full support 48Edge Full support 15Firefox Full support 48IE No support NoOpera Full support 35Safari Full support 10WebView Android Full support 48Chrome Android Full support 48Firefox Android Full support 48Opera Android Full support 35Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0

Legend

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参考