syntax:

object.isPrototypeOf(variable)

where:

variable - the object to test.

return:

boolean - true if variable is an object and the current object is present in the prototype chain of the object, otherwise it returns false.

description:

If variable is not an object, then this method immediately returns false. Otherwise, the method recursively searches the internal _prototype property of the object and if at any point the current object is equal to one of these prototype properties, then the method returns true.