ArrayBuffer[@@species]

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

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

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

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

class SubArrayBuffer extends ArrayBuffer {}
SubArrayBuffer[Symbol.species] === SubArrayBuffer; // true

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

The @@species property returns the default constructor function, which is the ArrayBuffer constructor for ArrayBuffer.

ArrayBuffer[Symbol.species]; // function ArrayBuffer()

In an instance of a custom ArrayBuffer subclass, such as MyArrayBuffer, the MyArrayBuffer species is the MyArrayBuffer constructor. However, you might want to overwrite this, in order to return parent ArrayBuffer objects in your derived class methods:

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

• ArrayBuffer
• Symbol.species