How to add properties to an existing object type in JavaScript?

By adding the properties to the existing type prototype, you can add new properties to existing type.

function Employee(firstName, lastName, id){

  this.firstName = firstName;

  this.lastName = lastName;

  this.id = id;

}

/* Adding two new properties to the existing type Employee */

Employee.prototype.organization="ABC";

Employee.prototype.location="Bangalore";

Above statements add two properties organization, location to the Employee type.

Find the below working application.

HelloWorld.js

function Employee(firstName, lastName, id){
  this.firstName = firstName;
  this.lastName = lastName;
  this.id = id;
}

/* Adding two new properties to the existing type Employee */
Employee.prototype.organization="ABC";
Employee.prototype.location="Bangalore";

var emp1 = new Employee("Krishna", "Majety", 123);

console.log("firstName : " + emp1.firstName);
console.log("lastName : " + emp1.lastName);
console.log("id : " + emp1.id);
console.log("organization : " + emp1.organization);
console.log("location : " + emp1.location);

Output

firstName : Krishna

lastName : Majety

id : 123

organization : ABC

location : Bangalore

New properties are reflected to the objects that created after adding these new properties to types.

HelloWorld.js

function print_employee_information(emp){
  console.log("\n************************");
  console.log("firstName : " + emp.firstName);
  console.log("lastName : " + emp.lastName);
  console.log("id : " + emp.id);
  console.log("organization : " + emp.organization);
  console.log("location : " + emp.location);
}

function Employee(firstName, lastName, id){
  this.firstName = firstName;
  this.lastName = lastName;
  this.id = id;
}

var emp1 = new Employee("Krishna", "Majety", 123);
print_employee_information(emp1);

/* Adding two new properties to the existing type Employee */
Employee.prototype.organization="ABC";
Employee.prototype.location="Bangalore";

var emp1 = new Employee("Ram", "Gurram", 5678);
print_employee_information(emp1);

Output

************************

firstName : Krishna

lastName : Majety

id : 123

organization : undefined

location : undefined

************************

firstName : Ram

lastName : Gurram

id : 5678

organization : ABC

location : Bangalore

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