How do I use instanceof in JavaScript?

How do I use instanceof in JavaScript?

The instanceof operator checks if an object is an instance of a specific class or constructor. For example, obj instanceof ClassName returns true if obj is an instance of ClassName.

Can you give me an example of using instanceof?

Sure! Here's an example:

class Animal {}
class Dog extends Animal {}

const myDog = new Dog();
console.log(myDog instanceof Dog); // true
console.log(myDog instanceof Animal); // true
console.log(myDog instanceof Object); // true

What happens if I use instanceof with a primitive type?

Using instanceof with a primitive type will return false. For example, 5 instanceof Number will return false because 5 is a primitive number, not an instance of the Number object.

Are there any limitations to using instanceof?

Yes, instanceof can only check against constructor functions and won't work with objects created from different execution contexts, like iframes.