Symbol.species

¥Value

众所周知的符号 Symbol.species。

¥The well-known symbol Symbol.species.

¥Description

[Symbol.species] 访问器属性允许子类覆盖对象的默认构造函数。这指定了有关如何复制实例的协议。例如，当你使用数组的复制方法时，例如 map()。map() 方法使用 instance.constructor[Symbol.species] 来获取构造新数组的构造函数。欲了解更多信息，请参阅 子类化内置函数。

¥The [Symbol.species] accessor property allows subclasses to override the default constructor for objects. This specifies a protocol about how instances should be copied. For example, when you use copying methods of arrays, such as map(). the map() method uses instance.constructor[Symbol.species] to get the constructor for constructing the new array. For more information, see subclassing built-ins.

[Symbol.species] 的所有内置实现都返回 this 值，该值是当前实例的构造函数。这允许复制方法来创建派生类而不是基类的实例 - 例如，map() 将返回与原始数组相同类型的数组。

¥All built-in implementations of [Symbol.species] return the this value, which is the current instance's constructor. This allows copying methods to create instances of derived classes rather than the base class — for example, map() will return an array of the same type as the original array.

¥Examples

¥Using species

你可能希望在派生数组类 MyArray 中返回 Array 对象。例如，当使用 map() 等返回默认构造函数的方法时，你希望这些方法返回父 Array 对象，而不是 MyArray 对象。species 符号可让你执行此操作：

¥You might want to return Array objects in your derived array class MyArray. For example, when using methods such as map() that return the default constructor, you want these methods to return a parent Array object, instead of the MyArray object. The species symbol lets you do this:

class MyArray extends Array {
  // Overwrite species to the parent Array constructor
  static get [Symbol.species]() {
    return Array;
  }
}
const a = new MyArray(1, 2, 3);
const mapped = a.map((x) => x * x);

console.log(mapped instanceof MyArray); // false
console.log(mapped instanceof Array); // true

¥See also

• Array[Symbol.species]
• ArrayBuffer[Symbol.species]
• Map[Symbol.species]
• Promise[Symbol.species]
• RegExp[Symbol.species]
• Set[Symbol.species]
• TypedArray[Symbol.species]