Easily Extend Javascript Prototypes

So you have a class in javascript and you want it to inherit from another class right?

You want the following

• to be able to call the parent class constructor as well as the child
• you want the child class to inherit all methods from the parent class
• you want to be able to call super on individual methods in the child class

If so, keep reading....

simple utility function for extending a class

function extend (base, constructor) {
  var prototype = new Function();
  prototype.prototype = base.prototype;
  constructor.prototype = new prototype();
  constructor.prototype.constructor = constructor;
}

Example parent class in this case Animal that has a name and makes noise

// parent class
function Animal (name) {
  this.animalName = name;
  console.log("////== Animal Constructor ==/////");
  console.log("An animal named " + name);
}

Animal.prototype.makeNoise = function (noise) {
  console.log("////== Animal makeNoise() ==////");
  console.log(noise + ", I can make noise...");
};

Ok, now we want to make a Dog class that inherits from Animal

function Dog (name) {
  // call the super
  Animal.call(this, name);
  console.log("////== Dog Constructor ==/////");
  console.log("I am a Dog named " + this.animalName);
}

// important that this happens before you override methods on parent class
extend(Animal, Dog);

Dog.prototype.makeNoise = function (noise) {
  Animal.prototype.makeNoise.call(this, noise);
  console.log("////== Dog makeNoise() ==////");
  console.log("I am a Dog, I like to " + noise);
};

So we now have a Dog that also has all the Animal methods. We would use it like so...

var dog = new Dog("Sparky");
dog.makeNoise("Bark!!");

And that would output

"////== Animal Constructor ==/////"
"An animal named Sparky"
"////== Dog Constructor ==/////"
"I am a Dog named Sparky"
"////== Animal makeNoise() ==////"
"Bark!!, I can make noise..."
"////== Dog makeNoise() ==////"
"I am a Dog, I like to Bark!!"

See example working
http://jsbin.com/zixohimo/1/edit?js,console