Objects and Methods in JavaScript

Monday, Feb 3, 2020

In a previous note, constructors were introduced as blueprints for creating objects. In addition to defining the state of objects, constructors can also define the behavior of objects through methods. Methods are functions but defined uniquely for a particular type of objects. This is the fundamental notion of object-oriented programming.

In the example below, I show this feature by creating a constructor called point (in 2d cartesian coordinates). Point's state is defined by two attributes - x and y. Following this, two methods are defined for point - it's distance from the origin through mag method and it's distance from another point through dist method:

Point and it's Methods

// describing methods for objects
function Point(x, y)            // point in 2d coordinates
    this.x = x;
    this.y = y;

    this.mag = function()       // distance from origin
        return Math.sqrt(this.x*this.x + this.y*this.y).toFixed(2)

    this.dist = function(other) // distance from another point
        x_sq = Math.pow((this.x - other.x), 2);
        y_sq = Math.pow((this.y - other.y), 2);
        return Math.sqrt(x_sq + y_sq).toFixed(2)

Let's test it

p1 = new Point(2, 3);
p2 = new Point(3, 4);