Why prototype is used in JavaScript?

JavaScript is a dynamic language and at any time we can add new properties to an object and can be shared among all the instances. Hence to add new properties and implement inheritance prototypes are used.

Example

function Candidate() {
    this.name = 'Arun';
    this.role = 'QA';
}
var candidateObj1 = new Candidate();
candidateObj1.salary = 10000;
console.log(candidateObj1.salary); // 10000
var candidateObj2 = new Candidate();
console.log(candidateObj2.salary); // undefined