I understand that inheritance in JavaScript can be accomplished with the following (copied from MDN):
// Shape - superclass
function Shape() {
this.x = 0;
this.y = 0;
}
// superclass method
Shape.prototype.move = function(x, y) {
this.x += x;
this.y += y;
console.info('Shape moved.');
};
// Rectangle - subclass
function Rectangle() {
Shape.call(this); // call super constructor.
}
// subclass extends superclass
Rectangle.prototype = Object.create(Shape.prototype);
Rectangle.prototype.constructor = Rectangle;
var rect = new Rectangle();
console.log('Is rect an instance of Rectangle? ' + (rect instanceof Rectangle)); // true
console.log('Is rect an instance of Shape? ' + (rect instanceof Shape)); // true
rect.move(1, 1); // Outputs, 'Shape moved.'
What I'm not understanding is why replacing:
Rectangle.prototype = Object.create(Shape.prototype);
Rectangle.prototype.constructor = Rectangle;
with:
Rectangle.prototype.prototype = Shape.prototype;
doesn't accomplish the same thing?
Performing a similar manipulation on an instance seems to work fine. Example:
var rect = new Rectangle();
rect.__proto__.__proto__ = Shape.prototype;
But manipulating prototypes this way is discouraged
