I'm a novice-to-intermediate JavaScript/jQuery programmer, so concrete/executable examples would be very much appreciated.

My project requires using AJAX to poll a URL that returns JSON containing either content to be added to the DOM, or a message { status : pending } that indicates that the backend is still working on generating a JSON response with the content. The idea is that the first request to the URL triggers the backend to start building a JSON response (which is then cached), and subsequent calls check to see if this JSON is ready (in which case it's provided).

In my script, I need to poll this URL at 15-second intervals up to 1:30 mins., and do the following:

• If the AJAX request results in an error, terminate the script.


• If the AJAX request results in success, and the JSON content contains { status : pending }, continue polling.


• If the AJAX request results in success, and the JSON content contains usable content (i.e. any valid response other than { status : pending }), then display that content, stop polling and terminate the script.

I've tried a few approaches with limited success, but I get the sense that they're all messier than they need to be. Here's a skeletal function I've used with success to make a single AJAX request at a time, which does its job if I get usable content from the JSON response:

// make the AJAX request

function ajax_request() {

  $.ajax({

    url: JSON_URL, // JSON_URL is a global variable

    dataType: 'json',

    error: function(xhr_data) {

      // terminate the script

    },

    success: function(xhr_data) {

      if (xhr_data.status == 'pending') {

        // continue polling

      } else {

        success(xhr_data);

      }

    },

    contentType: 'application/json'

  });

}

However, this function currently does nothing unless it receives a valid JSON response containing usable content.

I'm not sure what to do on the lines that are just comments. I suspect that another function should handle the polling, and call ajax_request() as needed, but I don't know the most elegant way for ajax_request() to communicate its results back to the polling function so that it can respond appropriately.

Any help is very much appreciated! Please let me know if I can provide any more information. Thanks!