Asynchronously load images with jQuery

Using jQuery you may simply change the "src" attribute to "data-src". The image won't be loaded. But the location is stored with the tag. Which I like.

<img class="loadlater" data-src="path/to/image.ext"/>

A Simple piece of jQuery copies data-src to src, which will start loading the image when you need it. In my case when the page has finished loading.

$(document).ready(function(){
    $(".loadlater").each(function(index, element){
        $(element).attr("src", $(element).attr("data-src"));
    });
});

I bet the jQuery code could be abbreviated, but it is understandable this way.

No need for ajax. You can create a new image element, set its source attribute and place it somewhere in the document once it has finished loading:

var img = $("<img />").attr('src', 'http://somedomain.com/image.jpg')
    .on('load', function() {
        if (!this.complete || typeof this.naturalWidth == "undefined" || this.naturalWidth == 0) {
            alert('broken image!');
        } else {
            $("#something").append(img);
        }
    });

IF YOU REALLY NEED TO USE AJAX...

I came accross usecases where the onload handlers were not the right choice. In my case when printing via javascript. So there are actually two options to use AJAX style for this:

Solution 1

Use Base64 image data and a REST image service. If you have your own webservice, you can add a JSP/PHP REST script that offers images in Base64 encoding. Now how is that useful? I came across a cool new syntax for image encoding:

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhE..."/>

So you can load the Image Base64 data using Ajax and then on completion you build the Base64 data string to the image! Great fun :). I recommend to use this site http://www.freeformatter.com/base64-encoder.html for image encoding.

$.ajax({ 
    url : 'BASE64_IMAGE_REST_URL', 
    processData : false,
}).always(function(b64data){
    $("#IMAGE_ID").attr("src", "data:image/png;base64,"+b64data);
});

Solution2:

Trick the browser to use its cache. This gives you a nice fadeIn() when the resource is in the browsers cache:

var url = 'IMAGE_URL';
$.ajax({ 
    url : url, 
    cache: true,
    processData : false,
}).always(function(){
    $("#IMAGE_ID").attr("src", url).fadeIn();
});   

However, both methods have its drawbacks: The first one only works on modern browsers. The second one has performance glitches and relies on assumption how the cache will be used.

cheers, will