How can I reliably preload and cache my ajax loading image across my site?

Question

I added the following code to my asp.net-mvc site.master page with the goal is making sure this image gets loaded upfront and cached (as I use it all over my site):

    $(document).ready(function () {

        var x = new Image();
        x.src = "/content/images/ajax-loader.gif";

I am assuming this code would force a preload and cache of this ajax loading image but when i run a page that references this image, i still see this for a few seconds. Here is an example of a jqgrid loading div

which uses this code for loadtext:

 $.jgrid = $.jgrid || {};
 $.extend($.jgrid,{
   defaults : {
    recordtext: "View {0} - {1} of {2}",
    emptyrecords: "No records to view",
    loadtext: "Loading Data ...<img src='/Content/Images/ajax-loader.gif' />",
    pgtext : "Page {0} of {1}"
},

before my actual ajax loading image shows like below:

Is there any suggestion for what could be causing this and how to ensure this image is loaded and cached prior to trying to use it? Is my solution actually redownloading the file each time?

What is the best recommendation here for how to achieve my goal?

Answer 1

Whenever you use an img element, the browser will request it from server. Using CSS background-image, will request the image only once, and you can use it multiple times, without seeing that problem again.

.loading {
  display: inline-block;
  width: 16px;
  height: 16px;
  background: url(http://i.stack.imgur.com/CRmPi.gif);
}

<div>Hello World <span class="loading"></span></div>
<div>Hello World <span class="loading"></span></div>
<div>Hello World <span class="loading"></span></div>

Answer 2

According to the specifications given by the W3C, URL's are in fact case-sensitive.

Of course, in a windows file system, case doesn't matter, so for the server these two are the same file

/content/images/ajax-loader.gif
/Content/Images/ajax-loader.gif

The server will serve the image regardless of what case you use (on Windows).

However, all browsers actually follow the specifications for URL's, and will treat those two URL's as two different resources.

To the browser, those are two different files, caching one won't cache the other.

In other words, you're caching one resources, and then loading a completely different resource, because you're not using the same case.

Make absolutely sure that you type the URL exactly the same, and genereally just using lowercase is the way to go

$(document).ready(function () {

    var x = new Image();
    x.src = "/content/images/ajax-loader.gif";

    $.jgrid = $.jgrid || {};
    $.extend($.jgrid,{
      defaults : {
        recordtext: "View {0} - {1} of {2}",
        emptyrecords: "No records to view",
        loadtext: "Loading Data ...<img src='/content/images/ajax-loader.gif' />",
        pgtext : "Page {0} of {1}"
     },
   .......