Question

I have a very quirky api that can only handle a single request at a time.
Therefore, I need to ensure that every time a request is made, it goes into a queue, and that queue is executed one request at a time, until it is empty.

Normally, I just use jQuery’s built in queue, since the site is already using jQuery. However, I was not sure if I could somehow decorate the $http service, or wrap it in another service that returns one promise at a time, or something else.

Answer 1

Here is my solution for that: http://plnkr.co/edit/Tmjw0MCfSbBSgWRhFvcg

The idea is: each run of service add request to queue and return promise. When request to $http is finished resolve/refuse returned promise and execute next task from queue if any.

app.factory('srv', function($q,$http) {

  var queue=[];
  var execNext = function() {
    var task = queue[0];
    $http(task.c).then(function(data) {
      queue.shift();
      task.d.resolve(data);
      if (queue.length>0) execNext();
    }, function(err) {
      queue.shift();
      task.d.reject(err);
      if (queue.length>0) execNext();
    })
    ;
  }; 
  return function(config) {
    var d = $q.defer();
    queue.push({c:config,d:d});
    if (queue.length===1) execNext();            
    return d.promise;
  };
});

Looks quite simple 🙂