JS Question
What is Prototype Chaining in JS?

Question

JS Question

What is Prototype Chaining in JS?

Accepted Answer

Answer :
1) Nearly all objects in JavaScript are instances of Object.

2) That means all the objects in JavaScript inherit the properties and methods from Object.prototype. This is called Prototype chaining.

3) This is a very powerful and potentially dangerous mechanism to override or extend object behavior.

4) Objects created using the new keyword inherit from a prototype called Object.prototype.
For example: If a date object [new Date()] is created with the new keyword, then it inherits the
Date.prototype.
We have Date, Array, Function, RegExp in the list for the same. All these objects inherit from the Object.prototype.

5) We should never alter or change the predefined methods or properties of a prototype, It may cause inappropriate failure, which may be difficult to debug.

6) To check whether the object has a property or not, we use "hasOwnProperty()" method. For example if we have the age property in any object, we can check it with the help of the hasOwnProperty() method.

Let’s take a look at a quick example of prototype chaining.

In this example, we will create a class and add a prototype object in the same. After instantiation of the object, we will be able to use the prototype of the class. This is simply object prototype chaining.

> function Person(firstName, lastName, age){
this.firstName = firstName;
this.lastName = lastName;
this.age = age;
}

//Person class created

Person.prototype.getFullName = function(){
return this.firstName + ” ” + this.lastName;
}

// we have added getFullName method in Person’s prototype.
> var person = new Person(“ross”, “gellar”, 25);
// It will create an instance of the Person class

> person.hasOwnProperty(“firstName”); // true
> person.hasOwnProperty(“getFullName”); // false

> person.getFullName(); // ross gellar

In the above code, we used hasOwnProperty() method to check whether we have getFullName method as a property of the object. It returned false, that means there is no such property. But, when we used getFullName method, it returned the actual full name but the property was not there.

Reason : As the getFullName() method was not there in the object but still we were able to use it. We should not forget that we added the method in class Person’s prototype. The method went to the object through prototype chaining. It means the class had the method in its prototype, which went to its instance (person object) through prototype chaining.

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