What is easy way to convert object in array Angular JS?

You don't need to convert object to array in order to iterate over it in ng-repeat. You can just use the following syntax:

<div ng-repeat="(key, value) in items">{{key}} => {{value}}</div>

Documentation of ngRepeat.

Unfortunately, this approach will not work with orderBy filter. To iterate over object properties in specific order, you need to implement your own filter. It may be something like that:

JavaScript

angular.module('app', []).
  filter('orderByKey', ['$filter', function($filter) {
    return function(items, field, reverse) {
      var keys = $filter('orderBy')(Object.keys(items), field, reverse),
          obj = {};
      keys.forEach(function(key) {
        obj[key] = items[key];
      });
      return obj;
    };
  }]);

HTML

<div ng-repeat="(key, value) in items | orderByKey:'-'">{{key}} => {{value}}</div>

Plunker

http://plnkr.co/edit/DJo0Y6GaOzSuoi202Hkj?p=preview

However even this approach will work only starting from 1.4.x, since as it is stated in documentation, AngularJS prior to 1.4.x will sort object properties in alphabetic order while iterating over them in ngRepeat.

In order to make it work in Angular 1.3.x or even 1.2.x you may perform conversion of object to array of objects, each one of which will contain key and value properties. That way you will be able to use it in ngRepeat in combination with filters including orderBy. Here is a code:

JavaScript

angular.module('app', []).
  factory('srv', ['$http', function($http) {
    var items = [],
        loaded = false;
    return {
      getItems: function() {
        if(!loaded) { // Lazy loading
          $http.get('data.json').success(function(data) { // {key1: 'val1', key2: 'val2'}
            Object.keys(data).forEach(function(key) {
              items.push({key: key, value: data[key]});
            });
          });
          loaded = true;
        }
        return items; // [{key: 'key1', value:'val1'}, {key:'key2', value: 'val2'}]
      }
    };
  }]).
  controller('ctrl', ['$scope', 'srv', function($scope, srv) {
    $scope.items = srv.getItems();
  }]);

HTML

<div ng-repeat="item in items | orderBy:'-key'">{{item.key}} => {{item.value}}</div>

Plunker

http://plnkr.co/edit/UXmlm1GKYRZzrOV5pMYT?p=preview

Let's say you have an object like:

$scope.myObj = {type:"Fiat", model:500, color:"white"};

Then, in your angular Controller you can do something like:

$scope.array = [];
angular.forEach($scope.myObj, function(element) {
  $scope.array.push(element);
});

and then in your HTML

<div ng-repeat="obj in array">{{obj}}</div>

Here is a demo plunker

orderBy is a filter, and filters require an array. So a straightforward solution is to combine it with a toArray filter. Supposing you want to order your objects using their time property:

<ol>
  <li ng-repeat="value in objectWithValues | toArray | orderBy: 'time'">
    {{value.name_user}} said <q>{{value.message}}</q> on {{value.time|date}}
  </li>
</ol>

As the toArray filter is not shipped with AngularJS, you can define one as:

angular.module('ToArrayDemo', [])
  .filter('toArray', function() {
    return function(obj) {
      const result = [];
      angular.forEach(obj, function(val) {
        result.push(val);
      });
     return result;
   }
 });

See https://plnkr.co/edit/E857InfrEGqToW0SvwOh?p=preview