Asynchronously load images with jQuery

问题

I want to load external images on my page asynchronously using jQuery and I have tried the following:

$.ajax({ 
   url: \"http://somedomain.com/image.jpg\", 
   timeout:5000,
   success: function() {

   },
   error: function(r,x) {

   }
});

But it always returns error, is it even possible to load image like this?

I tried to use .load method and it works but I have no idea how I can set timeout if the image is not available (404). How can I do this?

回答1:

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);
        }
    });

回答2:

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

回答3:

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.

回答4:

$(<img />).attr('src','http://somedomain.com/image.jpg');

Should be better than ajax because if its a gallery and you are looping through a list of pics, if the image is already in cache, it wont send another request to server. It will request in the case of jQuery/ajax and return a HTTP 304 (Not modified) and then use original image from cache if its already there. The above method reduces an empty request to server after the first loop of images in the gallery.

回答5:

You can use a Deferred objects for ASYNC loading.

function load_img_async(source) {
    return $.Deferred (function (task) {
        var image = new Image();
        image.onload = function () {task.resolve(image);}
        image.onerror = function () {task.reject();}
        image.src=source;
    }).promise();
}

$.when(load_img_async(IMAGE_URL)).done(function (image) {
    $(#id).empty().append(image);
});

Please pay attention: image.onload must be before image.src to prevent problems with cache.

回答6:

If you just want to set the source of the image you can use this.

$("img").attr('src','http://somedomain.com/image.jpg');

回答7:

This works too ..

var image = new Image();
image.src = 'image url';
image.onload = function(e){
  // functionalities on load
}
$("#img-container").append(image);

回答8:

AFAIK you would have to do a .load() function here as apposed to the .ajax(), but you could use jQuery setTimeout to keep it live (ish)

<script>
 $(document).ready(function() {
 $.ajaxSetup({
    cache: false
});
 $("#placeholder").load("PATH TO IMAGE");
   var refreshId = setInterval(function() {
      $("#placeholder").load("PATH TO IMAGE");
   }, 500);
});
</script>

回答9:

use .load to load your image. to test if you get an error ( let's say 404 ) you can do the following:

$("#img_id").error(function(){
  //$(this).hide();
  //alert("img not loaded");
  //some action you whant here
});

careful - .error() event will not trigger when the src attribute is empty for an image.

回答10:

$(function () {

    if ($('#hdnFromGLMS')[0].value == 'MB9262') {
        $('.clr').append('<img src="~/Images/CDAB_london.jpg">');
    }
    else
    {
        $('.clr').css("display", "none");
        $('#imgIreland').css("display", "block");
        $('.clrIrland').append('<img src="~/Images/Ireland-v1.jpg">');
    }
});

来源：https://stackoverflow.com/questions/4285042/asynchronously-load-images-with-jquery