jQuery Ajax call very slow in IE, but instant in Firefox

Question

I am performing a jQuery .ajax() call that returns a List<string> of IP addresses on a specified subnet. I use a [WebMethod] on an .aspx page to return the values. ASP.NET's built-in JSON serializer does the magic to return the actual JSON used in my Javascript.

I have profiled the the server-side time, and it takes about 8 msec to populate and return the list, so the server-side code is not the issue.

However, when the Ajax call is initiated, in Internet Explorer it can take upwards of 3 seconds to populate a listbox with a small list of IP addresses returned. In Firefox, the listbox is essentially populated instantly.

I'm not entirely certain where the bottleneck could be. My best guess is that the fault lies with IE6's javascript engine, but even so, adding only 255 list items should not take this much time.

Can anyone point me in the right direction as to why this is happening?

Example Code

$.ajax({
          type: "POST",
          url: $("Example.aspx/GetIPsOnNetwork",
          data: "{NetworkID: " + networkID + "}",
          contentType: "application/json; charset=utf-8",
          dataType: "json",
          success: function(data) {
            $('#ipAddresses').empty();
            // Loop through each IP address and add it to the listbox
            $.each(data.d, function(){
                var ip = this.toString();
                $(document.createElement('option')).attr('value', ip).text(ip).appendTo('#ipAddresses');
            });
          },
          error: function(msg) {
            alert('Error: ' + msg);
          }
        });

Answer 1

It could be a rendering issue. try this

      success: function(data) {
        // Loop through each IP address and add it to the listbox
        var list = $("<select />");
        $.each(data.d, function(){
            var ip = this.toString();
            list.append($('<option />').val(ip).text(ip));
        });
        $('#ipAddress').empty().append(list.find('option'));
      },

Basically, what you're doing is loading the options into a dummy list, then you're adding the contents to the ipAddresses list.

The other thing that I changed was the document.createElement(...). If you look at the internals of $('<option />') it performs the createElement for you.

Finally I choose to append the data to the list instead of calling option.appendTo('#ipAddress'), which would have to find the ipAddress element every time.

Answer 2

I suspect it might be a difference in speed of creating the option elements in IE and adding each one by one to the DOM.

On this line

$(document.createElement('option')).attr('value', ip).text(ip).appendTo('#ipAddresses');

You could try

var optionArray = [];
for (var i= 0; i < this.length; i++)
{
      optionArray[i] = $('<option>').val(ip).text(ip);
}
$('#ipAddresses').empty().append(optionArray.join(""));

or this (data.d is an object, right?)

var optionArray = [];
var i = 0;
$.each(data.d, function(key, value)
{
      optionArray[i++] = $('<option>').val(value).text(value);
});
$('#ipAddresses').empty().append(optionArray.join(""));

You might find this article on jQuery's append() useful

Answer 3

Creating elements using the recommended DOM creation methods is extremely slow compared to the non-standard yet ubiquitous .innerHTML property. I once had to update a table with about 100 rows and just like you experienced, the older the browser the slower the operation using element creation. If you can, create a dummy SELECT element and populate it with a manually a concatenated HTML string of your OPTION elements and then use .innerHTML on your dummy SELECT object. You are then free to do whatever you want with this element (using .replaceChild, etc).

While this is a non-standard way of doing element creation, .innerHTML is going to stay with us for a long, long time, and it is fast.

Answer 4

I've found jqueyry's append to be very slow compared to innerHTML in IE7. Firefox and Chrome seem to render at the same speed using either append or innerHTML. This may have something to do with what Salaryman was saying about DOM creation methods.