How to add a method to a JavaScript object?

Javascript Web Development Front End Technology

In this article, we’ll go over how to add a method to a JavaScript object in JavaScript with appropriate examples.

A JavaScript object is an entity which has properties. A property can be a variable or a method which define state and behavior of the object. A method is a property of an object that adds behavior to an object.

We can add a method to a JavaScript object using object prototype. All JavaScript objects get their attributes and methods from a prototype.

Let’s understand this concept better with the help of examples further in this article.

Syntax

The syntax to add a method to the JavaScript object using Object Prototype is −

functionName.prototype.newMethodName = function(){}
or
functionName.prototype.newMethodName = function(param1,param2,..paramN){}

Where,

functionName is the existing function name
newMethodName is the method name to be added.
param1, param2..paramN are the parameters that are to be passed to the new method.

Example 1

This is an example program to add a method to an object by extending the behavior of Calculator function prototype with add.

<html>
<head>
   <meta charset="UTF-8">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>To add a method to a JavaScript object.</title>
</head>
<body style="text-align : center">
   <h3>To add a method to a JavaScript object.</h3>
   <p id="method-to-obj"></p>
   <script>
      function Calculator(){
         Calculator.prototype.add = function (a,b){
            var result = a+b;
            document.getElementById('method-to-obj').innerHTML='The sum of two numbers is : '+result;
         }
      }
      var calc = new Calculator();
      calc.add(10,20);
   </script>
</body>
</html>

On executing the above code, the below output is generated.

Example 2

This is an example program to add a method to JavaScript object.

<!DOCTYPE html>
<html>
<head>
   <meta charset="UTF-8">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>To add a method to a JavaScript object.</title>
</head>
<body style="text-align : center">
   <h3>To add a method to a JavaScript object.</h3>
   <p id="method-to-obj"></p>
   <script>
      function Car(name, model, year, color) {
         this.Name = name;
         this.Model = model;
         this.Year = year;
         this.Color = color;
      }
      var car1 = new Car("Maruti", "Vitara Brezza", "2016", "Red");
      car1.prop = function() {
         return ""+this.Name+" has launched in the year "+this.Year;
      }
      document.getElementById("method-to-obj").innerHTML = car1.prop();
   </script>
</body>
</html>

On executing the above code, the below output is generated.

Example 3

This is an example program to create a function which returns an object. In this example, a .mul is created as a property of the object. Each of the new object created has a .mul function created for them. In this example, method is a parameter to the function.

<html>
<head>
   <meta charset="UTF-8">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>To add a method to a JavaScript object.</title>
</head>
<body style="text-align : center">
   <h3>To add a method to a JavaScript object.</h3>
   <p id="method-to-obj"></p>
   <script>
      function ReturnCalculatorObject() {
         var a, b,
         multiplication = function (a, b) {
            var result = a * b;
            document.getElementById('method-to-obj').innerHTML = 'The Product of two numbers is : ' + result;
         },
         object1 = {
            mul: multiplication
         };
         return object1;
         }
         var calc = new ReturnCalculatorObject();
         calc.mul(20, 30);
   </script>
</body>
</html>

On executing the above code, the below output is generated.