Experimental Page Flip Monitor module for CommandFusion iViewer

PageFlipMonitor.js

/* PageFlipMonitor v1.0
 * Copyright 2013 CommandFusion, public domain
 * 
 * Utility object that monitors entering and exiting pages,
 * and can call any number of callbacks specifically registered to observe
 * when entering or exiting a page
 *
 * You callback functions should be of the form:
 *
 function callback(fromPage, toPage) {
 	// do your processing here
 }
 *
 * To monitor page flips, call watchEnter or watchExit. Each function returns a unique ID that allows
 * you to later unregister the watch
 *
 * var watch1 = PageFlipMonitor.watchEnter("Page 1", myEnterCallback);	// be notified when entering "Page 1"
 * var watch2 = PageFlipMonitor.watchExit("Page 1", myExitCallback);		// be notified when exiting "Page 1"
 *
 * // to stop watching:
 *
 * PageFlipMonitor.unwatch(watch1);
 * PageFlipMonitor.unwatch(watch2);
 *
 */
var PageFlipMonitor = {
	nextID: 0,
    enter: {},
    exit: {},
	watchEnter: function(pageName, callback) {
		return this.register(this.enter, pageName, callback);
	},
	watchExit: function(pageName, callback) {
		return this.register(this.exit, pageName, callback);
	},
	unwatch: function(id) {
		function filter(watchSet) {
			for (var pageName in watchSet) {
				if (watchSet.hasOwnProperty(pageName)) {
					watchSet[pageName] = watchSet[pageName].filter(function(e) {
						return e.id != id;
					});
				}
			}
		}
		filter(this.enter);
		filter(this.exit);
	},

	// internal function, do not use
	register: function(watchSet, pageName, callback) {
		function doCallbacks(array, from, to) {
			if (array != null) {
				array.forEach(function(elem) {
					try {
						elem.cb.apply(null, from, to);
					}
					catch(e) {
						CF.log("Warning: exception caught while calling Page Flip callback from " + from + " to " + to + ": " + e);
					}
				});
			}
		}
	    var array = watchSet[pageName];
		if (array == null) {
			array = [];
			watchSet[pageName] = array;
		}
		if (this.nextID == 0) {
			var self = this;
			CF.watch(CF.PageFlipEvent, function(from, to) {
				if (from != null)
					doCallbacks(self.exit[from], from, to);
				if (to != null)
					doCallbacks(self.enter[to], from, to);
			});
		}
		var id = this.nextID++;
		array.push({
			id: id,
			cb: callback
		});
		return id;
	}
};