If you find yourself triggering the '$apply already in progress' error while developing with Angular.JS (for me I find I hit most often when integrating third party plugins that trigger a lot of DOM events), you can use a 'safeApply' method that checks the current phase before executing your function. I usually just monkey patch this into the $s…

safeApply.js

.factory('safeApply', ['$rootScope', function($rootScope) {
    return function($scope, fn) {
        var phase = $scope.$root.$$phase;
        if(phase == '$apply' || phase == '$digest') {
            if (fn) {
                $scope.$eval(fn);
            }
        } else {
            if (fn) {
                $scope.$apply(fn);
            } else {
                $scope.$apply();
            }
        }
    }
}])


.controller('MyCtrl', ['$scope,' 'safeApply', function($scope, safeApply) {
    safeApply($scope);                     // no function passed in
    safeApply($scope, function() {   // passing a function in
    });
}])