Events - only calls the first handler, unregisters them afterwards. * before.js shows the vanilla backbone implementation. * in model.js shows the helper function * after.js shows the new implementation.

after.js

action.oncefirst( {
	'cancel' : function(msg) {
		...
	},
	'error' : function(msg) {
		...
	},
	'complete;' : function(data) {
		...
	}
});
action.run(context);

before.js

var oncancel = function(msg) {
	...
	cleanup();
};
var onerror = function(msg) {
  ...
	cleanup();
};
var oncomplete = function(data) {
  ...
  cleanup();
};
var cleanup = function() {
	action.off('cancel', oncancel);
	action.off('error', onerror);
	action.off('complete', oncomplete);
};
action.on('cancel', oncancel);
action.on('error', onerror);
action.on('complete', oncomplete);
action.run(context);

in model.js

	/**
	 * Given an event map, register each event handler.
	 * 
	 * If any of those events are triggered, unregister all the given handlers.
	 * 
	 * Returns the unregister function - call if the given handlers should be removed before any are triggered. 
	 */
	oncefirst: function(listeners) {
		var unregister = function() { this.off(listeners); };
		this.once( _.keys(listeners).join(' '), unregister );
		this.on(listeners);
		return unregister;
	}