Say I have a base class "Pet" and child classes "Dog" and "Cat". Is there a generic way I can take an arbitrary object I know is a "Pet" and test to see if it is "Dog" or "Cat"?
You can either ask the object for its constructor.name property, or if you have a reference to the class, you can use the instanceof operator:
class Pet {
constructor(name) {
this.name = name;
}
}
class Cat extends Pet {
sayHello() { console.log(`${this.name} miaows`) }
}
class Dog extends Pet {
sayHello() { console.log(`${this.name} barks`) }
}
const goofy = new Dog('Pluto');
const garfield = new Cat('Garfield');
console.log(goofy.constructor.name);
console.log(garfield.constructor.name);
console.log(goofy instanceof Dog);
console.log(garfield instanceof Cat);Please note that Pet shouldn't know about the existence of Dog or Cat (and also neither of the latter two should know anything about the existence of the other).