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Load two images in a single img tag one after another

I want to load two images in a single <img /> tag. First small image will be shown by src attribute and second large image will be inside data-src attribute but one image will be shown at once, that will be in src attribute. I want when page load small image will be load and show first and after completing loading of large image in the background it will be replaced by small image so that we can see large image. I have the code that will take large image from data-src attribute and place large image in src attribute.
$(document).ready(function(){
$("#image4").load(function(){
var imgDefer = document.getElementsByTagName('img');
for (var i=0; i<imgDefer.length; i++) {
if(imgDefer[i].getAttribute('data-src')) {
imgDefer[i].setAttribute('src',imgDefer[i].getAttribute('data-src'));
} }
});
});
I want to do this because I don't want to wait for long time to load large image, instead I want to see the small image first. I am facing the problem when page load, it's loading small and large images in parallel. For your information images have the drag and zoom functionality.
Current live code is here: http://virtualepark.com/new1/demo.html

The code you posted here is not deployed on your server - there is some other stuff using the mousewheel-event.
Try loading the big image hidden in the background and once its loaded, set the url of the visible image:
//get all images
$('img').each(function(i, img) {
var img = $(img);
//if they have a data-src
if(img.attr('data-src')) {
//register for the load-event for the initial image
img.one('load', function() {
//if small image is loaded, begin loading the big image
//create new hidden image
var hiddenImg = new Image();
hiddenImg.onload = function() {
//if the hidden image is loaded, set the src-attribute of the
//real image (it will show instantly)
img.attr('src', img.attr('data-src'));
};
//trigger loading of the resource
hiddenImg.src = img.attr('data-src');
});
});
});
(credits to Load image from url and draw to HTML5 Canvas)

you can load to hidden tag and after load complet change them.

you can try to start the loading after the image is loaded.
$('img').load(function(){
var bigImgSrc = $(this).data('src');
var img = $(this);
if(bigImgSrc != img.prop('src')){
var bigImg =$('<img>').prop('src', bigImgSrc);
bigImg.load(function(){
img.prop('src', bigImgSrc);
});
}
});
I'm not 100% sure if you need to append the bigImg to the DOM or if it also loads like this. If you need to add it to the DOM use bigImg.hide().appendTo('body') and then use the remove funtion when loaded.
You should also be aware that the load-function not work in all cases, see https://api.jquery.com/load-event/
edit there was in an infinity loop in the prev. code example

Change loading order of images already on page

Is there any way without AJAX of changing the loading order of images on a page? Or even a way to completely halt or pause loading of images already present?
The use case is simple - I have a long list of images down a page, and visitors will be landing on different spots of the page using URL anchors (/images#middle-of-page) that refer to actual containers for those images.
I'd like in the least to load the images inside the requested container FIRST, then continue loading the rest of the images.
The challenge is that there is no way to know the image paths of the requested container image before loading the page DOM.
I've tried getting the container img contents on load, then using the Javascript new Image() technique, but it doesn't change the fact that that image on the page will still be waiting for all previous images to load.
I've also tried immediately prepending a div in the body with a background image (CSS) of said img path, but this also does not prioritize the image load.
Any other ideas?

You need to have a DOM with empty img placeholders, i.e.
<img src="" mysrc="[real image url here]" />
Or you can make images to display "Loading..." image by default. You can even cache real image url in some custom tag, mysrc for example. Then once you know what exactly images you want to show (and in what order) you need to build a sequence of image loading
var images = [];//array of images to show from start and in proper order
function step(i){
var img = images[i++];
img.onload = function(){
step(i);
}
img.src = "[some url here]"
}
Hope this helps.

For interest, this is the function I ended up implementing based on the answers here (I made it an on-demand loading function for optimum speed):
function loadImage(img) { // NEED ALTERNATE METHOD FOR USERS w/o JAVASCRIPT! Otherwise, they won't see any images.
//var img = new Image(); // Use only if constructing new <img> element
var src = img.attr('alt'); // Find stored img path in 'alt' element
if(src != 'loaded') {
img
.load(function() {
$(this).css('visibility','visible').hide().fadeIn(200); // Hide image until loaded, then fade in
$(this).parents('div:first').css('background','none'); // Remove background ajax spinner
$(this).attr('alt', 'loaded'); // Skip this function next time
// alert('Done loading!');
})
.error(function() {
alert("Couldn't load image! Please contact an administrator.");
$(this).parents('div:first').find("a").prepend("<p>We couldn't find the image, but you can try clicking here to view the image(s).</p>");
$(this).parents('div:first').css('background','none');
})
.attr('src', src);
}
}

The img loading="lazy" attribute now provides a great way to implement this.
With it, images load automatically only when on the viewport. But you can also force them to load by setting in the JavaScript:
document.getElementById('myimg').loading = 'eager';
I have provided a full runnable example at: How do you make images load lazily only when they are in the viewport?
One really cool thing about this method is that it is fully SEO friendly, since the src= attribute contains the image source as usual, see also: Lazy image loading with semantic markup

What is this simple javascript doing

I am reading a tutorial and keep getting stuck on the first line of code, I know "new" in php is to make an object, but this tutorial has nothing to do with that. please help
var img = new Image();
the tutorial is here:
http://jqueryfordesigners.com/image-loading/
Ok, I found the W3 definition of the predefined javascript object Image(): http://www.w3schools.com/jsref/dom_obj_image.asp

Actually, in JavaScript new is used when making objects too, just like PHP.
As you can guess, therefore, that line of code simply instantiates an Image object and assigns it to the img variable.

this has nothing to do with jQuery.
Image is a native JavaScript object which corresponds to a HTML image object.
what the line means, is
"create a new variable 'img' and set it to a newly initialised Image object"

you can preload an image with
var img = new Image();
they preload the image images/headshot.jpg
then they wait until it has been loaded
then thay hide the loading image and fade in the image

It's make an html form for you.
for detail read this http://www.devguru.com/technologies/ecmascript/quickref/image.html
Hope this might help you a lot.
or you want to know it create
var img = new Image();
and not use?
$(img)
// once the image has loaded, execute this code
.load(function () {
// set the image hidden by default
$(this).hide();
// with the holding div #loader, apply:
$('#loader')
// remove the loading class (so no background spinner),
.removeClass('loading')
// then insert our image
.append(this);
// fade our image in to create a nice effect
$(this).fadeIn();
})
// if there was an error loading the image, react accordingly
.error(function () {
// notify the user that the image could not be loaded
})
// *finally*, set the src attribute of the new image to our image
.attr('src', 'images/headshot.jpg');
});
The 'this' keyword is represent for img variable

How to load an image asynchronously?

I'm loading an image onto a texture map with GLGE (sorta like webGl). However for the sake of loading speed I'm loading a low resolution image first (which would be quicker) and then want to change the src to the high resolution image once the large image is loaded. This is what I'm doing now
var texture = new GLGE.texture();
function updateTexture(){
var image=new Image();
image.src = "models/testLargeMap_map0.jpg"; // load image
image.onload = function(){
texture.image("models/testLargeMap_map0.jpg"); // supposedly swap image on load (not working as I thought)
}
}
However, when during this period of changing the src, the model and all its functions freeze. How do I make it load the image asynchronously and on load swap it to the higher texture for a smooth instantaneous texture change?

You can set an image.onload event handler like this:
var big_image = new Image();
big_image.onload = function () {
texture.image("models/testLargeMap_map0.jpg");
}
big_image.src = "models/testLargeMap_map0.jpg";
(Note that I set the onload handler first, then set the src attribute. If I do it the other way around, it fails in IE).
This will preload the image before calling texture.image. I don't know anything about this library though, so I can't be certain it will use the pre-loaded image.

The image.src will be requesting the image from the server and it will initiate the onload event, and again u are requesting the image to be swapped so it is getting freezed. Why do you need this approach. You can have better way of doing this like, allow the low resolution image to be loaded first then assign the onmouseover or onclick event for the image on that time u can show a popup like shown on google images and then in it just display the high resolution images. On that time u will be requesting a single image the process will be quicker.
Hope this helps you

I'm not familiar with "GLGE" but it looks like the problem is that the method .image() loads the image again (kind regardless if that happens in the load event handler for the same image).
So unless you can set the image reference directly, like
texture = this; // within the load handler
there is no way to accomplish it with this library.

Changing <img src="XXX" />, js event when new image has finished loading?

I have a photo gallery web page where a single <img src="XXX" /> element's src is changed (on a click) with JavaScript to show the next image—a poor man's ajax I guess. Works great on faster connections when the new image appears almost immediately. Even if it takes a few seconds to load, every browser I've tested it on keeps the old image in place until the new one is completely loaded.
It's a little confusing waiting those few seconds on a slow connection, though, and I'm wondering if there's some JavaScript event that fires when the new image is done loading, allowing me to put a little working... animated gif or something up in the meantime.
I know I could use AJAX for real (I'm using jQuery already), but this is such a nice and simple solution. Besides this lag, is there any other reason I should stay away from this approach to changing images?

You can set up a handler on the "load" event.
$('img.whatever')
.load(function() { /* do stuff */ })
.attr('src', newURL);
Actually I guess you'd want to do this with "live()":
$('img.reloadable').live('load', function() { $(this).show(); });
// ...
$('img#someId').hide().attr('src', newURL);
edit — whoa, where did that year go? Well, it turns out that one problem with that "live" approach I typed in way back when is that the "load" event does not bubble. Now what you can do, however, is leverage the way that "Image" objects (as opposed to <img> DOM elements) behave. Basically, the function that changes the URL can use an "Image" element as the place to keep the handler. The code that changes the actual "src" attribute of the real <img> tag would then also update the "src" of the "Image" object instance. The browser will only really load the image once (assuming cache control is all cool), but the browser will still call the "onload" handler of the "Image":
(function() {
var imageObj = new Image();
imageObj.onload = function() {
// code to run when image loads from server
};
$('#hypotheticalButton').click(function() {
$('#imgToUpdate').attr('src', newURL);
imageObj.src = newURL;
});
})();

You just just preload the images with jQuery so that way when the user clicks, the next image is already loaded and there shouldn't be a delay...that is unless the user goes to your page, and starts clicking on the image before they are loaded.
http://engineeredweb.com/blog/09/12/preloading-images-jquery-and-javascript

var slideimg = $('#slideimage');
slideimg.click(function(){
var img = new Image();
var url = 'url_to_next_image.jpg';
$(img).bind('load',function(){
$('#loading').hide();
slideimg.attr('src',url);
}).attr('src',url);
$('#loading').show();
});
This should work even with IE's crazy cache handling.