The Object isPrototypeOf() Method: Explained and Demonstrated

The isPrototypeOf() method in JavaScript is a powerful tool for determining if an object is in the prototype chain of another object. By calling this method on an object instance and passing in another object as an argument, you can quickly check if the object being called on is a prototype of the argument object. The method returns true if the object is found in the prototype chain, and false if it is not.

Let’s look at an example to understand how this works:

const Animal = {
    isAnimal: true
}

const Mammal = Object.create(Animal)
Mammal.isMammal = true

Animal.isPrototypeOf(Mammal) // true

const dog = Object.create(Animal)
Object.setPrototypeOf(dog, Mammal)

Animal.isPrototypeOf(dog) // true
Mammal.isPrototypeOf(dog) // true

In the code above, we have defined an object Animal with a single property isAnimal. We then create a new object Mammal using Object.create() and set its prototype to Animal. We also add an additional property isMammal to Mammal.

Next, we create a new object dog using Object.create() and set its prototype to Animal using Object.setPrototypeOf(). This means that dog has both Animal and Mammal as part of its prototype chain.

When we call Animal.isPrototypeOf(Mammal), it returns true because Animal is indeed in Mammal’s prototype chain. Similarly, when we call Animal.isPrototypeOf(dog) and Mammal.isPrototypeOf(dog), both return true since both Animal and Mammal are in dog’s prototype chain.

Using the isPrototypeOf() method gives us a straightforward way to check if an object is a prototype of another object. It is particularly useful when working with inheritance and object hierarchies in JavaScript.

Tags: JavaScript, object prototype, isPrototypeOf()