How to add properties and methods to an object in JavaScript?

To add properties and methods to an object in JavaScript, use the prototype property.

Example

You can try to run the following code to learn how to work with prototype −

<html>
   <head>
      <title>JavaScript prototype property</title>
      <script>
         function book(title, author) {
            this.title = title;
            this.author = author;
         }
      </script>
   </head>
   <body>
      <script>
         var myBook = new book("Amit", "Java");
         book.prototype.price = null;
         myBook.price = 500;

         document.write("Book title is : " + myBook.title + "<br>");
         document.write("Book author is : " + myBook.author + "<br>");
         document.write("Book price is : " + myBook.price + "<br>");
      </script>
   </body>
</html>