angular.toJson 是把一个对象转换成Json字符串。
angular.fromJson是从一个Json字符串解析出一个对象或者对象数组。

例如：

  if($rootScope.loginData == null && $rootScope.rolesList == null){$.ajax({url: config.loginUrl, type: "POST", dataType: "json", cache: false, async: false,xhrFields: {withCredentials: true},data: null,success: function (data) {if(data && angular.fromJson(data.data).access_token != null){//此处的$rootScope.loginData充当定义对象的作用，必须使用fromJson，使用toJson则会报错。$rootScope.loginData = angular.fromJson(data.data);//设置cookie值的时候，需要字符串，而不是对象，所有使用toJsonsetCookie('loginDate',angular.toJson($rootScope.loginData), 0);$.ajax({url: config.userInfoUrl + "?userCode=" + ($rootScope.loginData.userCode), type: "GET", dataType: "json", cache: false, async: false,xhrFields: {withCredentials: true},beforeSend: function(request) {//request.setRequestHeader();},data: null,success: function (userInfo) {angular.extend($rootScope.loginData, userInfo);setCookie('loginDate',angular.toJson($rootScope.loginData), 0);$.ajax({                    url: config.userGradeInfo +"/"+ $rootScope.loginData.userCode, type: "GET", dataType: "json", cache: false, async: false,xhrFields: {withCredentials: true},beforeSend: function(request) {//request.setRequestHeader();},data: null,success: function (userGrades) {$rootScope.rolesList = userGrades.data;var postData = angular.copy($rootScope.loginData);angular.extend(postData, userGrades.data);setCookie('rolesList',angular.toJson($rootScope.rolesList), 0);},error: function (status) {setCookie('loginDate',"");messageBox.alert("请刷新重试", "error");$timeout(function(){window.location.reload();}, 5000);}});},error: function (status) {setCookie('loginDate',"");messageBox.alert("获取用户信息出错，请刷新重试", "error");$timeout(function(){window.location.reload();}, 5000);}});}else{messageBox.alert("验证登录信息失败：access_token为空，点击确定重新登录")}},error: function (status) {console.log(status);}});}