JavaScript: Extends

extends.js

/* Base class */
function Shape() {

    this.area = function() { throw 'Abstract method'; };
}

/* Extends Shape */
function Rectangle(width, height) {

    var parent = new Shape();
    for(var p in parent) this[p] = parent[p];

    this.width = width;
    this.height = height;

    var _privateMethod = function() {
        return 'Private string. Width = ' + this.width;
    }.bind(this);

    this.publicMethod = function() {
        return _privateMethod();
    };

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

/* Extends Rectangle */
function Square(side) {

    var parent = new Rectangle(side, side);
    for(var p in parent) this[p] = parent[p];

    this.side = side;

    this.area = function() {
        return this.side * this.side;
    };

    this.hypotenuse = function() {
        return Math.sqrt(this.area() + this.area());
    }
}

var square = new Square(100);

console.log(square.hypotenuse());

console.log(square instanceof Square); // true
console.log(square instanceof Rectangle); // false

console.log(square.publicMethod()); // Private string. Width = 100