Ember unknownProperty & setUnknownProperty hooks defined inside Ember.Observable mixin

ember_unknown_property_hook.js

// Little background about unknown properties
var myObject = Ember.Object.create({name: 'hi'}); // a plain simple ember object

/*
  all the properties defined on the object are known properties 
  so the property "name" is a known property for myObject, 
  but any other properties which are not defined on this object are unknown properties 
*/
// age is an unknown property as we did not set "age" yet
myObject.get("age"); // => undefined

/* 
  Be careful ! only properties on the object that are not "set" yet are unknown properties,
  but not the properties that evaluate to null/undefined
*/
myObject.set("status", undefined); // although myObject.get("status") evaulates to undefined, status is a known property for myObject

/* 
 unknownProperty hook
 Basically when we do a "get" on a unknown property, 
 instead of returning undefined the result of the unknownProperty hook is returned
*/
var hookedObject = Ember.Object.create({
  name: 'Bruce Wayne',
  unknownProperty: function(key) {
    return key+" is an unknown property";
  }
});

hookedObject.get("name"); // => Bruce Wayne
hookedObject.get("randomKey"); // => randomKey is an unknown property
hookedObject.get("age"; // => age is an unknown property
hookedObject.set("age", 22); // age is now  a known property
hookedObject.get("age"); // => 22

/* 
  setUnknownProperty hook
 it gets called when we are trying to do a set on an unknown property
*/
var baseObject = Ember.Object.create();
var hookedObject = Ember.Object.create({
  setUnknownProperty: function(key, value){
    baseObject.set(key, value);
  }
});
hookedObject.set("name", "Bruce");
baseObject.get("name"); // => Bruce

/* 
  We are basically proxying the set property to other object, Reminds you of something ?...
  Enter Ember.ObjectProxy
   `Ember.ObjectProxy` forwards all properties not defined by the proxy itself
    to a proxied `content` object. (from the source code)
  Let's implement a similar proxy object of our own using the above concepts
*/
var myProxyObject = Ember.Object.create({
  unknownProperty: function(key){
    var content = this.get("content");
    if(content){
      return content.get(key);
    }
  },
  setUnknownProperty: function(key, value){
    var content = this.get("content");
    if(content){
      return content.set(key, value);
    }else{
      // raise an error saying cannot set key, value as the content property is undefined
    }
  }
})