Question

UPDATE Following @Ryan Olds suggestion to include the setTimeout in the callback, I must clarify that in my production code I’m calling multiple urls to get json data from several sites. (Have updated JavaScript code below).

Is it only possible to have multiple timeouts scattered throughout this function?

---

I have a self-invoking updateFunction as follows:

(function update() {
  $.ajax({
    type: 'GET',
    url: "http://myexample.com/jsondata",
    dataType: 'json',
    success: function (data) {
      // do some callback stuff
    },
    async: false
  });

 $.ajax({
    type: 'GET',
    url: "http://myexample2.com/jsondata2",
    dataType: 'json',
    success: function (data) {
      // do some further callback stuff
    },
    async: false
  });

  setTimeout(update, 2000);
})();

What I expected this code to do

I hoped that this function would go off to the target URL and wait for the result, then deal with the success callback. Then (and only then) would it fall through to set a 2 second timeout to call the function again.

What appears to be happening instead

Instead, the GET request codes out, and before the response has been dealt with, the timeout has already been set.

What am I missing? How can I make this entirely synchronous?

Answer 1

If I were you, I’d make use of jQuery’s support for deferred action.

(function update() {
    $.when($.ajax({
        type: 'GET',
        url: "http://myexample.com/jsondata",
        dataType: 'json',
        success: function (data) {
            // do some callback stuff
        }
    }), $.ajax({
        type: 'GET',
        url: "http://myexample2.com/jsondata2",
        dataType: 'json',
        success: function (data) {
            // do some further callback stuff
        }
    }), $.ajax({
        // more requests as you like
    })).then(function() {
        // when all the requests are complete
        setTimeout(update, 2000);
    });
}());

Much nicer, IMHO, than mucking around with synchronous requests. Indeed, if the requests are cross-domain, this is pretty much your only option.

See

• $.when
• deferred.then