No Peeking in the Javascript Deque

Another (previous) take on the Javascript Deque with more of a Crockford creation style preventing messing with the Deque's internals. Create one without using new - "var d = deque();", enjoy:

	// Javascript Doubly Ended Queue
	var deque = function() {
	var node = function(data, prev, next) {
	var that = {};
	that.data = data;
	that.prev = prev;
	that.next = next;
	return that;
	}
	var that = {};
	var head = node(null);
	var tail = node(null, head);
	head.next = tail;
	that.empty = function() {return head.next === tail;};
	that.push = function(data) {
	var n = node(data, tail.prev, tail)
	tail.prev.next = n;
	tail.prev = n;
	};
	that.pop = function() {
	if (that.empty()) {
	throw new Error("pop() called on empty deque");
	} else {
	var n = tail.prev;
	tail.prev = n.prev;
	tail.prev.next = tail;
	return n.data;
	}
	};
	that.unshift = function(data) {
	var n = node(data, head, head.next);
	head.next.prev = n;
	head.next = n;
	};
	that.shift = function() {
	if (that.empty()) {
	throw new Error("shift() called on empty deque");
	} else {
	var n = head.next;
	head.next = n.next;
	head.next.prev = head;
	return n.data;
	}
	};
	return that;
	};

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