JavaScript Object/Dictionary that keeps track of insertion order, allowing iteration in such order

orderPreservingObject.js

//	deploytonenyures.blogspot.com

//At the time of this writing (2014/07/22) this code only works in Firefox

//notice that at the time of this writing, Direct Proxies and Array.prototype.findIndex are only supported by Firefox
function OrderPreservingObject(initObj){
	var obj = {
		orderedKeys: [],
		forEach: function(actionFunc){
			//where actionFunc receives as parameters: item, key, tiedDic
			//I've chose this item-key order over key-item based on Array.protoype.forEach, that is passing: the element value, the element index, the array being traversed
			for(var i=0; i<this.orderedKeys.length; i++){
				var key = this.orderedKeys[i];
				actionFunc(this[key], key, this);
			}
		}
		// __iterator__: function* (){
			// for (var i=0; i<this.orderedKeys.length; i++){
				// yield this.orderedKeys[i];
			// }
		// }
	};
	//to prevent orderedKeys from showing up when iterating with "for in" we should declare it as non enumerable, 
	//but anyway, we should not use "for in" for iterating this object
	//ideally we would have managed to trap the "for in" and we would exclude it directly there
	var proxy = Proxy(obj, {
		//receiver is the proxy itself
		set: function(target,name,val,receiver){    
			//console.log("set invoked");
			target[name] = val;
			if (target.orderedKeys.findIndex(function(it){
				return it == name;
			}) == -1){
				target.orderedKeys.push(name);
			}
			return true;
		},
		deleteProperty: function(target,name){
			//console.log("delete invoked");
			delete target[name];
			var index = target.orderedKeys.findIndex(function(it){
				return it == name;
			});
			if (index != -1){
				target.orderedKeys.splice(index, 1);
			}
			return true;
		}, 
		//not completely sure how it works... so let's stick to keys
		// enumerate: function* (target){
			// console.log("enumerate invoked");
			// for (var i=0; i<target.orderedKeys.length; i++){
				// yield target.orderedKeys[i];
			// }
		// },
		
		keys: function(target){
			//console.log("keys invoked");
			return target.orderedKeys;
		}
	});
	//now that the proxy is set up, we can add the items in the initObj and they'll be added in order
	if (initObj){
		for (var key in initObj){
			proxy[key] = initObj[key];
		}
	}	
	return proxy;
}

//let's test it:

var dic1 = new OrderPreservingObject({
	name: "Xuan",
	city: "Berlin",
	age: 45
});

console.info("dic1.keys: " + Object.keys(dic1).join(", "));

delete dic1.city;

console.info("dic1.keys: " + Object.keys(dic1).join(", "));
dic1.job = "journalist";
console.info("dic1.keys: " + Object.keys(dic1).join(", "));

console.log("--------------");

for (var i=0; i<Object.keys(dic1).length; i++){
	var key = Object.keys(dic1)[i];
	console.info(key + " - " + dic1[key]);
}

console.log("--------------");

for (var i = 0; i< dic1.orderedKeys.length; i++){
	var key = dic1.orderedKeys[i];
	console.info(key + " - " + dic1[key]);
}

console.log("--------------");

dic1.forEach(function(item, key){
	console.info(key + " - " + item);
});

console.log("--------------");

//the __iterator__ fails to compile
// for (var key of dic1){
	// console.info(key + " - " + dic1[key]);
// }

console.log("--------------");

//I can't make the enumerate trap work
// for (var key in dic1){
	// console.info(key + " - " + dic1[key]);
// }