AJAX best practices?

https://news.ycombinator.com/item?id=37154

by morris • 19 years ago

7 19 19 years ago

news.ycombinator.com

I'm new to the AJAX business and am trying to find a resource outlining the basics. In particular, I'm very concerned with handling out of order asynchronous requests, but can't seem to find a very solid recommendation on how to handle them. As of now I'm going to implement a queuing system for dynamic requests but would rather not re-invent the wheel...

palish8• 19 years ago

One way to handle it is to design your system so that it doesn't matter if the requests come back out of order. Could you give an example of where order matters, so we can work on designing it so that order doesn't matter?

morris7• 19 years ago

I'd like to implement a note-taking system, with an auto-save feature (say, set by a timer). If the requests that go out to the server are received out of order, the wrong state will be auto-saved.

palish8• 19 years ago

Don't save again until the first save has been registered. If it times out, try again.

jey3• 19 years ago

What's the specific problem? Why do you need the results to be ordered? If you really do need to order the results, just attach a sequential ID to each request, then hold a priority queue of results sorted by request ID. Pseudo-code follows:

  next_request_id = 0;
  next_response_id = 0;

  // the following code assumes there's a PriorityQueue class implementing a
  // priority queue with push(object, priority) and pop() operations
  response_queue = new PriorityQueue();

  function send_request(request) {
      request.request_id = next_request_id;
      next_request_id++;
      ajax_send(request);
  }

  function receive_response(response) {
      response_queue.push(response, response.request_id);

      while(!response_queue.empty()
              && response_queue.top().request_id == next_response_id) {
          handle_response(response_queue.pop());
          next_response_id++;
      }
  }

The above code isn't very robust as it doesn't deal with requests that die in transit and never return a response, etc.

morris7• 19 years ago

Right - this is what I'm about to try to implement (and I think I'd trash the entire queue if a response isn't returned within some timeout limit and display a subsequent error message). I don't know if this is the best practice though and as this seems like a pretty generic AJAX problem, it feels like there should be a pretty generic solution...

jey3• 19 years ago

I doubt most AJAX applications are that reliant on request/response ordering. However, a priority queue is the generic solution. :-)

AJAX best practices?

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