jQuery loading images with complete callback

Question

I saw a comment on Ben Nadel's blog where Stephen Rushing posted a loader, but I can't figure out how I can pass the selectors and parameter...

I think I also need a completeCallback and errorCallback functions?

function imgLoad(img, completeCallback, errorCallback) {
    if (img != null && completeCallback != null) {
        var loadWatch = setInterval(watch, 500);
        function watch() {
            if (img.complete) {
                clearInterval(loadWatch);
                completeCallback(img);
            }
        }
    } else {
        if (typeof errorCallback == "function") errorCallback();
    }
}
// then call this from anywhere
imgLoad($("img.selector")[0], function(img) {
    $(img).fadeIn();
});

HTML:

<a href="#" class="tnClick" ><img id="myImage" src="images/001.jpg" /></a>

JS:

$(document).ready(function() {
    var newImage = "images/002.jpg";
    $("#myImage").css("display","none");
    $("a.tnClick").click(function() {
        // imgLoad here
    });
})

Answer 1

If you want it to load before showing, you can trim that down a lot, like this:

$(document).ready(function() {
    var newImage = "images/002.jpg"; //Image name

    $("a.tnClick").click(function() {
      $("#myImage").hide() //Hide it
        .one('load', function() { //Set something to run when it finishes loading
          $(this).fadeIn(); //Fade it in when loaded
        })
        .attr('src', newImage) //Set the source so it begins fetching
        .each(function() {
          //Cache fix for browsers that don't trigger .load()
          if(this.complete) $(this).trigger('load');
        });
    });
});

The .one() call makes sure .load() only fires once, so no duplicate fade-ins. The .each() at the end is because some browsers don't fire the load event for images fetched from cache, this is what the polling in the example you posted is trying to do as well.

Answer 2

You need to be careful when using the load event for images since if the image is found in the browser's cache IE and (I am told) Chrome will not fire the event as expected.

Since I had to face this problem myself, I solved by checking the DOM attribute complete (said to be working in most major browsers): if equals to true I just unbinded the previously bound 'load' event. See example:

$("#myimage").attr("src","http://www.mysite.com/myimage.jpg").load(doSomething);

if ($("#myimage").get(0).complete) {

    // already in cache?
            $("#myimage").unbind("load");
            doSomething();


}

Hope this helps