Question

I have a page with some checkboxes and a submit button. I use AJAX to post the checkbox values to a PHP script, calc.php, run some calculations with the data and assign the result to a PHP session variable. I have another PHP script, json.php, that takes that session data and encodes it as JSON for the jquery to display in the div. My problem is I allow the user to set the amount of data sets they are going to submit, subnumber, and my display loop gets out of sync when the user changes the number of sets.

For example, if they start with 3 data sets, they submit them one by one by pressing #button. After the last set, if (count == max) runs and. Now they can do another calculation and change the number of data sets if they wish. If they change it to say 2, output goes to four instead of reseting to 1 and emptying #log.

$("#button").click(function() {
$.ajax({
  type: "POST",
  url: "calc.php",
  data: $("form#checkboxes").serialize(),
  success: function(data) {
    if(document.getElementById('calc').checked) {
    var max = checkboxes.subnumber.value;
    var stop = Number(max) + 1;
    count++;
    output++;
    $.getJSON('json.php', function(data) {
      $.each(data, function(key, val) {
        $('#log').append(output);
        $('#log').append(val.result);
        $('#log').append("</br>");
      })
    })
    if (count == max){
      count = 0;
      $("#results").load('results.php')
    }
if(output == stop) {
  $("#log").empty();
  output = 1;
}
}
}
})
}

I know it’s something simple, but I have been trying to fix it for two hours now and can’t figure out the problem. Everything else works perfectly, it’s just the output counter that isn’t done correctly.

Answer 1

You’re running asynchronous calls into your JSON. If users are doing things so quickly that the calls are coming back out of order, the issue lies in there.

You’ve got two options:

1. Run all of your JSON synchronously (use async:false in your JSON calls)
2. Utilize a counter and only process events that are coming back on the current index.

Psuedo Code for #2:

var pCounter = 0;
function doSomeAjax()
{
    pCounter++;
    $.ajax('url',{
        data:{count:pCounter}
        success:function(data)
            {
                // your json should return the current counter index
                if (data.counter != pCounter) return;
                // execute normally.
            }
    });
}