rx.js

function() {
	var videos = [
		{
			"id": 65432445,
			"title": "The Chamber"
		},
		{
			"id": 675465,
			"title": "Fracture"
		},
		{
			"id": 70111470,
			"title": "Die Hard"
		},
		{
			"id": 654356453,
			"title": "Bad Boys"
		}
	];

	// Expecting this output...
	// [
	//     {
	//         "65432445": "The Chamber",
	//         "675465": "Fracture",
	//         "70111470": "Die Hard",
	//         "654356453": "Bad Boys"
	//     }
	// ]
	return videos.
		reduce(function(accumulatedMap, video) {

			// Object.create() makes a fast copy of the accumulatedMap by
			// creating a new object and setting the accumulatedMap to be the
			// new object's prototype.
			// Initially the new object is empty and has no members of its own,
			// except a pointer to the object on which it was based. If an
			// attempt to find a member on the new object fails, the new object
			// silently attempts to find the member on its prototype. This
			// process continues recursively, with each object checking its
			// prototype until the member is found or we reach the first object
			// we created.
			// If we set a member value on the new object, it is stored
			// directly on that object, leaving the prototype unchanged.
			// Object.create() is perfect for functional programming because it
			// makes creating a new object with a different member value almost
			// as cheap as changing the member on the original object!

			var copyOfAccumulatedMap = Object.create(accumulatedMap);

			copyOfAccumulatedMap[video.id] = video.title;

			return copyOfAccumulatedMap;
		},
		// Use an empty map as the initial value instead of the first item in
		// the list.
		{});
}