Good evening! Here's our prompt for today.

In Object-Oriented programming, an instance represents an object which is an instantiation of a class. An object can also be an instance of a given class A if it is instantiated from a class B that extends the class A.

In a non-programming context, you could think of "cat" as a class and your particular cat as an instance of that class.

Many object-oriented programming languages have a built-in way of checking if a given object is an instance of a given class, and in Javascript this can be achieved by checking if the prototype property of a constructor appears anywhere in the prototype chain of an object.

Can you implement a function that will check if an object is an instance of a class, and will accept the object and the class as parameters?

The function should work like the following example:

1class A {}
2class B extends A {}
3
4let objB = new B()
5instanceOfClass(objB , B) // true
6instanceOfClass(objB, A) // true
7
8class C {}
9instanceOfClass(objB, C) // false

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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function instanceOfClass(obj, targetClass) {

    if (!obj || typeof obj !== 'object') return false

    if (!target.prototype) throw Error

​

    if (Object.getPrototypeOf(obj) === target.prototype) {

        return true

    } else {

        return instanceOfClass(Object.getPrototypeOf(obj), target)

    }

}

​

Here's our guided, illustrated walk-through.

How do I use this guide?