Check $dirty/$prestine state of an angular model.

$dirtyCheck.js

(function () {
    'use strict';

    function $dirtyCheck(){
    	var watchers = [],
    	    dirty = false;
    	return {
    		add: function($scope, model){
    			if ($scope && model){
    				var watcher = $scope.$watch(model, function(isDirty) {
			            if (isDirty){
			            	dirty = true;
			            }
			        });
			        watchers.push(watcher);
    			}
    		},
    		clear: function(){
    			//De-register watchers
    			angular.forEach(watchers, function(watcher){
    				watcher();
    			});
    			watchers = [];
    			dirty = false;
    		},
    		check: function(){
    			return dirty;
    		}
    	}
    }

    angular
        .module('APP_NAME')
        .service('$dirtyCheck', $dirtyCheck);

})();