How to preload JSON data so its available when Angularjs module is ready - json

Question

I have a very simple app that loads a JSON array using $http.get inside of a controller. It assigns the result data to scope and the HTML repeats through the results to display a list. It is a very simple angularjs example.
function ViewListCtrl($scope, $http) {
$scope.shoppinglist = [];
$scope.loadList = function () {
var httpRequest = $http({
method: 'POST',
url: 'viewList_service.asp',
data: ''
}).success(function (data, status) {
$scope.shoppinglist = data;
});
};
$scope.loadList();
}
While testing on a slow server I realized there was a 3 second blocking delay while rending the repeat region. Debugging revealed to me that my controller does not attempt to get the data until the page is loaded. My page takes 3 seconds to load. Then I must wait another 3 seconds for the json data to load.
I want to load data as soon as possible so it is ready when my controller is ready. Simply put, I want to pre-load the data so it loads in parallel to my module.
I've searched all over and the closest thing I found was "resolve", but I am not using routes. This is a very simple list and no routes or templates.
How can I load the JSON as soon as the page starts to render so it is ready when the controller is ready and there is no blocking... and then get that data into scope?

Answer 1

You can use the module.run method. Which is executed after the config stage is completed. To make use of this you need to create a service factory that does the actual query and caches the result
module("myapp",[]).factory('listService', function($q,$http) {
var listData;
var defer = $q.defer();
return {
loadList: function() {
if(listData) {
defer.resolve(listData);
}
else {
var httpRequest = $http({
method: 'POST',
url: 'viewList_service.asp',
data: ''
})
.success(function(data) {
listData=data;
defer.resolve(listData);
}
}
return defer.promise;
}
}
});
In your controller you still use the factory to get the data with a promise then wrapper.
listService.loadList().then(function(data) {
$scope.shoppinglist=data;
});
This way you can make the async call even before any controller related code executes.

Answer 2

You can load data by writing code (something like Chandermani's listService) in separate file but without using angular. you can use jquery ajax to load your data.
Then write a service in angular to read that data and pass it to your controller.

Answer 3

It sounds like your latency comes from a slow network + server, and not a large amount of data.
So, you could render a tag into your page, so that the data would be sent along with the page HTML response. The downside there is that you're hard-coding your data into your page. This tag would basically pre-seed the $http cache with your data.
var listJson = {...json data here, rendered server-side...};
mod.run(function($cacheFactory) {
var cache = $cacheFactory('yourListCacheId');
cache.put('list-cache-id', listJson);
// store "cache" somewhere you can retrieve it, such as a service or value.
});
Then either use the $http cache property, or wrap $http in a custom service which checks the cache.
Of course, the root of the problem is that your server takes 3 seconds per request, when you normally want that at least in the sub-second range.