SharedArrayBuffer[@@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 buffer.

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

// Hypothetical underlying implementation for illustration
class SharedArrayBuffer {
  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 SharedArrayBuffer {}
SubArrayBuffer[Symbol.species] === SharedArrayBuffer; // true

When calling array buffer methods that do not mutate the existing array but return a new array buffer instance (for example, slice()), the array'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 SharedArrayBuffer constructor for SharedArrayBuffer.

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

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

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

• SharedArrayBuffer
• Symbol.species