Book Image

Learning Object-Oriented Programming

By : Gaston C. Hillar
Book Image

Learning Object-Oriented Programming

By: Gaston C. Hillar

Overview of this book

Table of Contents (16 chapters)
Learning Object-Oriented Programming
About the Author
About the Reviewers

Creating instances in JavaScript

We already created instances with the simple Rectangle constructor function. We just needed to use the new keyword and the constructor function name. We then need to specify the required arguments enclosed in parentheses and assign the result to a variable.

The following lines declare a new version of the Rectangle constructor function that adds a calculateArea function to the blueprint:

function Rectangle(width, height) {
    console.log("I'm creating a new Rectangle");
    this.width = width;
    this.height = height;

    this.calculateArea = function() {
        return this.width * this.height;

The new constructor function adds a parameterless calculateArea method to the instance. The following lines of code create a new Rectangle object named rectangle3 and then print the results of the call to the calculateArea method for this object:

var rectangle3 = new Rectangle(143, 187);

If we enter the following line, the JavaScript...