Javascript focus tree eventing

focustree.js

focustree = (function() {
	var entries = [];
	var currentFocus = [];
	
	function indexOf(array, element) {
		for (var i = 0; i < array.length; i++) {
			if (array[i] === element) return i;
		}
		return -1;
	}
	function removeAll(a, b) {
		var result = [];
		for (var i = 0; i < a.length; i++) {
			if (indexOf(b, a[i]) < 0) result.push(a[i]);
		}
		return result;
	}
	function contains(element) {
		for (var i = 0; i < entries.length; i++) {
			if (entries[i].element === element) return true;
		}
		return false;
	}
	function descendants(start) {
		var result = [];
		var node = start;
		while (node != null) {
			if (contains(node)) result.push(node);
			node = node.parentNode;
		}
		return result;
	}
	
	function fireIn(element, event) {
		var entry = register(element);
		for (var i = 0; i < entry.in.length; i++) {
			entry.in[i]();
		}
	}
	function fireOut(element, event) {
		var entry = register(element);
		for (var i = 0; i < entry.out.length; i++) {
			entry.out[i]();
		}
	}
	
	function onfocus(event) {
		var newFocus = descendants(event.srcElement);
		
		var elementsIn = removeAll(newFocus, currentFocus);
		for (var i = 0; i < elementsIn.length; i++) {
			fireIn(elementsIn[i], event);
		}
		var elementsOut = removeAll(currentFocus, newFocus);
		for (var i = 0; i < elementsOut.length; i++) {
			fireOut(elementsOut[i], event);
		}
		
		currentFocus = newFocus;
	}
	function onblur(event) {
	}
	
	function init() {
		document.body.addEventListener("focus", onfocus, true);
		document.body.addEventListener("blur", onblur, true);
	}
	
	function register(element) {
		var i;
		for (i = 0; i < entries.length; i++) {
			if (entries[i].element === element) break;
		}
		if (i < entries.length) return entries[i];
		var entry = {element: element, in: [], out: []};
		entries.push(entry);
		return entry;
	}
	
	function registerIn(element, callback) {
		var entry = register(element);
		entry.in.push(callback);
	}
	function registerOut(element, callback) {
		var entry = register(element);
		entry.out.push(callback);
	}
	
	return {init: init, registerIn: registerIn, registerOut: registerOut};
})();