Symbol.species

The Symbol.species static data property represents the well-known symbol Symbol.species. Methods that create copies of an object may look up this symbol on the object for the constructor function to use when creating the copy.

Warning: The existence of [Symbol.species] allows execution of arbitrary code and may create security vulnerabilities. It also makes certain optimizations much harder. Engine implementers are investigating whether to remove this feature. Avoid relying on it if possible.

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.