类型化数组[@@物种]

¥Syntax

TypedArray[Symbol.species]

¥Return value

调用 get @@species 的构造函数 (this) 的值。返回值用于从创建新类型化数组的类型化数组方法构造返回值。

¥The value of the constructor (this) on which get @@species was called. The return value is used to construct return values from typed array methods that create new typed arrays.

¥Description

@@species 访问器属性返回 类型数组 对象的默认构造函数。子类构造函数可以重写它以更改构造函数赋值。默认实现基本上是：

¥The @@species accessor property returns the default constructor for typed array objects. Subclass constructors may override it to change the constructor assignment. The default implementation is basically:

// Hypothetical underlying implementation for illustration
class TypedArray {
  static get [Symbol.species]() {
    return this;
  }
}

由于这种多态实现，派生子类的 @@species 也会默认返回构造函数本身。

¥Because of this polymorphic implementation, @@species of derived subclasses would also return the constructor itself by default.

class SubTypedArray extends Int8Array {}
SubTypedArray[Symbol.species] === SubTypedArray; // true

当调用不改变现有数组但返回新数组实例（例如 filter() 和 map()）的类型化数组方法时，将访问该数组的 constructor[@@species]。返回的构造函数将用于构造类型化数组方法的返回值。

¥When calling typed array methods that do not mutate the existing array but return a new array instance (for example, filter() and map()), the array's constructor[@@species] will be accessed. The returned constructor will be used to construct the return value of the typed array method.

然而，与 Array[@@species] 不同，当使用 @@species 创建新的类型化数组时，该语言将确保新创建的数组是正确的类型化数组，并且具有与原始数组相同的内容类型 - 例如，你不能创建 BigInt64Array 从 Float64Array 创建一个非 BigInt 数组，或者从 BigInt 数组创建一个非 BigInt 数组。这样做会抛出 TypeError。

¥However, unlike Array[@@species], when using @@species to create new typed arrays, the language will make sure that the newly created array is a proper typed array and has the same content type as the original array — for example, you can't create a BigInt64Array from a Float64Array, or create a non-BigInt array from a BigInt array. Doing so throws a TypeError.

class BadArray extends Int8Array {
  static get [Symbol.species]() {
    return Array;
  }
}
new BadArray(1).map(() => 0); // TypeError: Method %TypedArray%.prototype.map called on incompatible receiver [object Array]

class BadArray2 extends Int8Array {
  static get [Symbol.species]() {
    return BigInt64Array;
  }
}
new BadArray2(1).map(() => 0n); // TypeError: TypedArray.prototype.map constructed typed array of different content type from |this|

注意：由于 SpiderMonkey 和 V8 中的错误，未检查内容类型匹配。在第二个示例中，只有 Safari 会抛出 TypeError。

¥Note: Due to a bug in both SpiderMonkey and V8, the content type match is not checked. Only Safari will throw a TypeError in the second example.

¥Examples

¥Species in ordinary objects

@@species 属性返回默认构造函数，它是任何给定 类型数组 构造函数的类型化数组构造函数本身之一。

¥The @@species property returns the default constructor function, which is one of the typed array constructors itself for any given typed array constructor.

Int8Array[Symbol.species]; // function Int8Array()
Uint8Array[Symbol.species]; // function Uint8Array()
Float32Array[Symbol.species]; // function Float32Array()

¥Species in derived objects

在自定义 TypedArray 子类（例如 MyTypedArray）的实例中，MyTypedArray 种类是 MyTypedArray 构造函数。但是，你可能想要覆盖它，以便在派生类方法中返回父 类型数组 对象：

¥In an instance of a custom TypedArray subclass, such as MyTypedArray, the MyTypedArray species is the MyTypedArray constructor. However, you might want to overwrite this, in order to return a parent typed array object in your derived class methods:

class MyTypedArray extends Uint8Array {
  // Overwrite MyTypedArray species to the parent Uint8Array constructor
  static get [Symbol.species]() {
    return Uint8Array;
  }
}

¥See also

• TypedArray
• Symbol.species