Set[@@species]

The value of the constructor (this) on which get @@species was called. The return value is used to construct copied Set instances.

The @@species accessor property returns the default constructor for Set objects. Subclass constructors may override it to change the constructor assignment.

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

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

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

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

• Set
• Symbol.species