jsprototypical.js

// A minimal polyfill for Object.assign
// (an ES6 feature)
Object.assign = Object.assign || function(){
  for(var i = 1; i < arguments.length; i++){
    for(var j in arguments[i]){
      arguments[0][j] = arguments[i][j];
    }
  }
};

// JavaScript has prototypical inheritance
// so there is no real difference in extending
// something or creating a new instance
// (although the new keyword may have tricked you
// into thinking so)

// A small Base object with a simple extend method
var Base = {
  extend: function(props){
    // A new object with this object as its prototype
    var obj = Object.create(this);
    // Assign properties to the new object
    Object.assign(obj,props);
    return obj;
  }
}

var Animal = Base.extend({
  alive: true,
  breath: function(){
    return "I take a breath";
  }
});


var Mammal = Animal.extend({
  run: function(){
    return "I run";
  }
});

var Human = Mammal.extend({
  name: "John Doe",
  write: function(){
    return this.name + " says: I'm trying to write something!"
  }
});

var Kalle = Human.extend({
  name: "Kalle"
});

var Eva = Human.extend({
  name: "Eva"
});

console.log(Kalle.write());
console.log(Eva.write());