Javascript Prototype

prototype is a most important part of the JavaScript. If you create the object then property and method of this object always inherit from the prototype.

function Student(first_name, last_name, age){
     
this.firstName=first_name;

this.lastName=last_name;

this.age=age;

}

var stu1 = new Student("John","Mathew",35);
console.log(stu1);

Output:-

Student {firstName: "John", lastName: "Mathew", age: 35}
age: 35
firstName: "John"
lastName: "Mathew"
__proto__:
constructor: ƒ Student(first_name, last_name, age)
__proto__:
constructor: ƒ Object()
hasOwnProperty: ƒ hasOwnProperty()
isPrototypeOf: ƒ isPrototypeOf()
propertyIsEnumerable: ƒ propertyIsEnumerable()
toLocaleString: ƒ toLocaleString()
toString: ƒ toString()
valueOf: ƒ valueOf()
__defineGetter__: ƒ __defineGetter__()
__defineSetter__: ƒ __defineSetter__()
__lookupGetter__: ƒ __lookupGetter__()
__lookupSetter__: ƒ __lookupSetter__()
get __proto__: ƒ __proto__()
set __proto__: ƒ __proto__()

Prototype is used to add property or method after created the constructor function.

Suppose you have Student constructor function which have 3 parameters first_name, last_name and age.

function Student(first_name, last_name, age){
     
this.firstName=first_name;

this.lastName=last_name;

this.age=age;

}

Now, you want to add new property class after created the constructor function.

Student.class="MCA";
var stu1 = new Student("John","Mathew",35);
console.log(stu1.class);

Now, you will use prototype to add into property after created the constructor function.

Example:-

Student.prototype.class="MCA";
var stu1 = new Student("John","Mathew",35);
console.log(stu1.class);

Student.address= function(){
	
 return 'Laxmi Nagar, New Delhi';

}

var stu1 = new Student("John","Mathew",35);
console.log(stu1.address);

Now, you will add prototype in the method after created the constructor function

Student.prototype.address= function(){
	
	return 'Laxmi Nagar, New Delhi';

}

var stu1 = new Student("John","Mathew",35);
console.log(stu1.address());

Javascript Prototype – Interview Questions

Javascript Prototype – Objective Questions (MCQs)