Add a property to a JavaScript object constructor?

Javascript Web Development Front End Technology

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

Adding a property to an object constructor is different from adding a property to a normal object. If we want to add a property, we have to add it in the constructor itself rather than outside the constructor whereas we can add anywhere in a normal object.

To get a better understanding of the given task, let’s look into the syntax and usage of the constructor in JavaScript.

Syntax

The syntax for a constructor is −

Constructor(); // No parameters
Constructor(param1); //One parameter constructor
Constructor(param1,param2,…,paramN) // N-parameter constructor.

Where param1,param2,..paramN are the parameters passed to the constructor.

Example 1

This is an example program to add a property to the JS Object constructor. In this example, we are adding parameter as a property to the constructor.

<!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 Constructor.</title>
</head>
<body style="text-align : center">
   <h3>Add a method to a JavaScript Object Constructor.</h3>
   <p id="prop-to-obj"></p>
   <script>
      function Car(name, model, year, color) {
         this.Name = name;
         this.Model = model;
         this.Year = year;
         this.Color = color;
         this.type = 'SUV'
      }
      var car1 = new Car("Maruti", "Vitara Brezza", "2016", "Red");
      document.getElementById("prop-to-obj").innerHTML = car1.Name+" is of "+car1.type+" type";
   </script>
</body>
</html>

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

Example 2

This is an example program to add a method as a property to the JS object contructor. We can add a function to object as a property. Then they can be referred as method.

<!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 Constructor.</title>
</head>
<body style="text-align : center">
   <h3>Add a method to a JavaScript Object Constructor.</h3>
   <p id="method-to-obj-constructor"></p>
   <script>
      function Car(name, model, year, color) {
         this.Name = name;
         this.Model = model;
         this.Year = year;
         this.Color = color;
         this.type = 'SUV';
         this.description = function() {
            return this.Name+" is of "+this.Model+" model and launched in the year "+this.Year+" and is of "+this.type+" type."
         }
      }
      var car1 = new Car("Maruti", "Vitara Brezza", "2016", "Red");
      document.getElementById("method-to-obj-constructor").innerHTML = car1.description();
   </script>
</body>
</html>

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

Example 3

This is an example program to add properties (method and parameter) to a JavaScript Object Constructor.

<!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 Constructor.</title>
</head>
<body style="text-align : center">
   <h3>Add a method to a JavaScript Object Constructor.</h3>
   <p id="method-to-obj-constructor"></p>
   <script>
      function Student(name, rollNo, course) {
         this.Name = name;
         this.RNo = rollNo;
         this.course = course;
         this.year = "2022";
         this.college = "St. Xaviers College";
         this.studentDetails = function () {
            return this.Name + " with roll number " + this.RNo + " is a student of : " + this.college;
         }
      }
      var studentObj = new Student("Harsha", "17355B07C7", "CSE");
      document.getElementById("method-to-obj-constructor").innerHTML = studentObj.studentDetails();
   </script>
</body>
</html>

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