Why does onload cause my image switch to flicker? - javascript

For some reason, when I use the attribute onload on my img tag, it causes my images to flicker. Ideally, when I load the page, an image is displayed and when I refresh the page, the image is changed.
Here's my tag as well as the function for it:
HTML
<img id="randomimage" onload="randomImg()" src="images/carmainpic.jpg" alt="main pic of car"/>
JavasScript
function randomImg(){
var images=["images/carmainpic.jpg","images/carmainpic2.jpg","images/carmainpic3.jpg"];
var num=Math.floor(Math.random()*3);
document.getElementById("randomimage").src=images[num];
}

Because the function you're calling changes the image's src to a random pick from the array, triggering a new load event, which changes the src randomly again, etc. On at least some browsers the cycle probably stops when you happen to assign the URL the image already has, too.
If your goal is to just show one of those images, at random, you can do that by leaving src off the img entirely and then adding it (once) with script (either immediately following the img in order to avoid your layout having to be adjusted when you add it, or in script at the end of the page if you prefer; no need to wait for any event):
<img id="randomimage" alt="main pic of car"/>
<script>
(function() {
var images=["images/carmainpic.jpg","images/carmainpic2.jpg","images/carmainpic3.jpg"];
var num=Math.floor(Math.random() * images.length); // <== Note change, so adding images to the array Just Works
document.getElementById("randomimage").src=images[num];
})();
</script>
Even if you put the script immediately after the <img ...> tag, the img element will be available to the script. So your choice whether to do it inline or with the other scripts at the end of the page.

The randomImg function is called every time the image loads. You can use a flag variable to make sure that you only change the image once:
var changed = false;
function randomImg(){
if (!changed) {
changed = true;
var images=["images/carmainpic.jpg","images/carmainpic2.jpg","images/carmainpic3.jpg"];
var num=Math.floor(Math.random()*3);
document.getElementById("randomimage").src=images[num];
}
}

The problem is that you are listening to the load event on the image, instead of the page.
onload="randomImg()"
So, as soon as the first image loads, it triggers the function randomImg which causes change of src attribute on the image. So the browser will attempt to assign a new image to the element, and yet another load event is triggered, which repeats the entire cycle.
Instead, if you want to choose a random image when the page loads, you can listen to DOMContentLoaded event on the document, and choose a random image.
document.addEventListener("DOMContentLoaded", function() {
var images=["images/carmainpic.jpg","images/carmainpic2.jpg","images/carmainpic3.jpg"];
var num=Math.floor(Math.random()*3);
document.getElementById("randomimage").src=images[num];
console.log("Showing: " + images[num]);
});
<img id="randomimage" src="images/carmainpic.jpg" alt="main pic of car"/>
Note: Since you are selecting a random image, it is not guaranteed that you will always get a different image when the page is refreshed. Instead, if you must get a different image on refreshing the page, you can perhaps persist the image identifier in localStorage, and use that to determine the next image to display.

Well you can use $(document).ready(function(){}) to do that. Because you want when charge the page that function execute it.
$(document).ready(function(){
function randomImg(){
var images=["https://www.bensound.com/bensound-img/romantic.jpg","https://www.psdstack.com/wp-content/uploads/2016/10/featured-copyright-free-mages.jpg","http://shaebaxter.com/wp-content/uploads/2015/04/Life-of-Pix-free-stock-photos-sea-peaople-water-waves-back-Sunset-Joshua-earle-1024x682.jpg"];
var num=Math.floor(Math.random()*3);
document.getElementById("randomimage").src=images[num];
}
randomImg();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<img id="randomimage" src="" alt="main pic of car"/>

Related

Javascript: Using onmouseover and onmouseout functions on more than one image

Edit: Sorry if I reply late to any solutions because I need time to figure out how they work haha
I am a beginner in Javascript and I am currently trying to use this piece of code to change an image on mouseover
// Mouseover change (Ciel):
function rollover(my_image){
my_image.src = "images/ci2_a.png";
}
function mouseaway(my_image){
my_image.src = "images/ci_a.png";
}
and this is the corresponding HTML
<img src="images/ci_a.png" onmouseover="rollover(this)" onmouseout="mouseaway(this)" alt="xxx" style="float:left; width:38%">
This works fine, but I want to do it for more than one image on the same page (a different image rollover for each picture) . Even after changing the name of the functions and stuff it doesn't work. The first image stops changing onmouseover immediately when I try to add a similar function for the next image. Could someone tell me how to perform similar events on more than one image (not concurrently)? Thank you!
You could add event listeners to all the image elements you'd like.
<img class="my-image" src="images/ci_a.png" onmouseover="rollover(this)" onmouseout="mouseaway(this)" alt="xxx" style="float:left; width:38%"/>
function rollover(){
this.src = "images/ci2_a.png";
}
function mouseaway(){
this.src = "images/ci_a.png";
}
const myImages = document.querySelectorAll('.my-image')
myImages.forEach(img => {
img.addEventListener('mouseenter', rollover)
img.addEventListener('mouseleave', mouseaway)
})
You can send the image file as the second parameter like this:
function rollover(element, image) {
element.src = image
}
...
<img onmouseover="rollover(this, 'images/ci2_a.png')" ...>
But my question is why do you need JavaScript for that? You can use a simple CSS to achieve this.
Since you need different images on load and on hover, you need a single way to define this functionality across a collection of images.
Building on Matthew's approach, here's a way to do that.
JSFiddle to test it real-time.
You'll dynamically generate the images using data attributes to store the alternate (hover) image URL.
<img class="pics" src="https://picsum.photos/id/0/100"
data-swap="https://picsum.photos/id/10/100">
<br>
<img class="pics" src="https://picsum.photos/id/1/100"
data-swap="https://picsum.photos/id/11/100">
<br>
<img class="pics" src="https://picsum.photos/id/2/100"
data-swap="https://picsum.photos/id/12/100">
<br>
<img class="pics" src="https://picsum.photos/id/3/100"
data-swap="https://picsum.photos/id/14/100">
Then define the event listeners for all elements with the class pics. Here's a list of all the events that can be referenced.
On mouseover, store the original image in a data element original.
Then change the src with the value of the data-swap.
On mouseout, replace the src with the original value.
const myImages = document.querySelectorAll('.pics')
myImages.forEach(img => {
img.addEventListener('mouseover', function () {
img.dataset.original = img.src;
img.src = img.dataset.swap;
});
img.addEventListener('mouseout', function () {
img.src = img.dataset.original;
});
})

JS load image on click

I need to load an image, js need to get link url and print this image on screen.
But it is not working.
What is wrong with my script? what can I do to make it work and improve it?
html
<div id=img></div>
<div id=loading></div>
<a href=http://png-5.findicons.com/files/icons/1580/devine_icons_part_2/128/my_computer.png class=postmini>Open image 1</a>
<br>
<a href=http://www.iconshock.com/img_jpg/BETA/communications/jpg/256/smile_icon.jpg class=postmini>Open image 2</a>
js
$(function() {
$(".postmini").click(function(){
var element = $(this);
var I = element.attr("href");
$("#loading").html('<img src="loader.gif" align="absmiddle"> loading...');
$("#loading").ajaxComplete(function(){}).slideUp();
$("#img").append(I);
});
});
https://jsfiddle.net/u6j2udzb/
and this loading div, what I need to do to make it work properly?
You are missing a lot and have a lot you don't need. I have commented out where you don't need items. In particular you don't need a loading because the image will be there before they see that. However, if you do want it still, you should be loading it underneath the image you are loading. So it gets covered by the image. I can update it with that if you'd like.
What you are missing is actual code to turn the href into an image source and you are not removing the default action of the anchor tag so it doesn't try loading a new page when clicked.
$(".postmini").click(function(event){
event.preventDefault();
var element = $(this);
var I = element.attr("href");
//$("#loading").html('loading...');
//$("#loading").ajaxComplete(function(){}).slideUp();
// remove old image if it is already there.
$("#img").empty();
// create variable holding the image src from the href link
var img = $("<img/>").attr("src", I)
$("#img").append(img);
});
https://jsfiddle.net/3g8ujLvd/
You just have to insert an img tag into your "display div" on click on the link... to load the image... (btw your syntax errors are terrible... you have to use quotes for attributes^^)
like this for example :
$('.postmini').on('click',function(){
//do something
});
Check this : https://jsfiddle.net/u6j2udzb/8/
(done quickly for example)
Hope it helps
You are not running an ajax script. ajaxComplete is only fired after an ajax script completed.
Whenever an Ajax request completes, jQuery triggers the ajaxComplete
event. Any and all handlers that have been registered with the
.ajaxComplete() method are executed at this time.
You should ad an ajax script and than ajaxComplete will run if you registered the ajaxComplete method.
At the moment you're just placing the text from the "href" attribute on the link into the div. You need to either create an image or use the link provided as a background.
The quickest way to see this is to change make this change:
var element = $(this);
var I = element.attr("href");
$("#loading").html('<img src="loader.gif" align="absmiddle"> loading...');
$("#loading").ajaxComplete(function(){}).slideUp();
// $("#img").append(I);
$("#img").html("<img src='"+I+"' />");
$('.postmini').on('click',function(e){
e.preventDefault();
$('#loading').html('<img src="'+this.href+'">').children('img').one('load',function(){$(this).parent().slideUp('slow');});
});
Noticed I used on instead of click this allows you to use this.href rather than a more lengthy $(this).attr('href'). I also used .one on a child image element to find out if the image has loaded.
But I've just realised that this is useless because you want to have a loader. Ma bad.
$('.postmini').on('click',function(e){
e.preventDefault();
//best have the loader.gif showing on default before the load is complete.
var img=$('<img class="loadedImage">');
img.src=this.href;
//img.css({display:none;});//remove this if you've enter CSS .loadedImage{display:none;}
$('#loading').append(img).slideDown('slow',function(){$(this).children('.loadedImage').one('load',function(){$(this).fadeIn('slow');$(this).siblings('img[src="loader.gif"]').hide();});});
});
This method is what you're looking for. Basically you want to click the link, stop the default action of going to the link, make a new image element and set the src, make sure it's hidden before load, add the new image element to loading, slide up parent loading, check for load and fade in :)
Try and run this simple snippet
$('#myButton').click(()=>{
let imgUrl = $('#imgUrl').val();
$.get(imgUrl)
.done(() => {
$('img').attr('src', imgUrl);
$('#imgText').text('');
})
.fail(() => {
$('#imgText').text('Image does not exist');
$('img').attr('src', '');
})
})
img {
width: 100%;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Image url: <input type="text" id="imgUrl" value="https://upload.wikimedia.org/wikipedia/commons/7/75/Woman_mechanic_working_on_engine_%28cropped%29.jpeg"><br>
<button id="myButton" type="button">click here to load image</button>
<div id="imgText"></div>
<img>

JavaScript tasks

I have been learning JavaScript and I have been doing some tasks, which I got in my college.
Tasks go like this:
Make a webpage, where 3 200x150 images and one 600x450 image will appear. Add JavaScript function, which will make sure, that the 600x450 image shown will be an enlarged image of an 200x150 image, on which we have pointed with a mouse previously (call the function with onMouseOver).
The second task goes like this:
Complete the webpage from task 1 in a way, when clicking the smaller image, the bigger image of the same image, we clicked will appear in a new window.
The code for the 1st task looks like this:
function bigImg(x)
{
x.style.height="600px";
x.style.width="450px";
}
function normalImg(x)
{
x.style.height="200px";
x.style.width="150px";
}
...
<img onmouseover="bigImg(this)" onmouseout="normalImg(this)" border="0" src="slika1.jpg" alt="slika1" width="150" height="200">
<img src="slika2.jpg">
<img src="slika3.jpg">
For the 2nd one like this:
function swipe()
{
var largeImage = document.getElementById('Slika1');
largeImage.style.display = 'block';
largeImage.style.width=450+"px";
// enter code here
var url=largeImage.getAttribute('src');
window.open(url,'Image','width=largeImage.style.width,height=largeImage.style.height,resizable=1');
}
...
<img src="slika1.jpg" id= "Slika1" onClick="swipe();"/>
<img src="slika2.jpg">
<img src="slika3.jpg">
What should be done differently?
<script>
function swipe(image)
{
newWidth=450+"px";
newHeight=600+"px";
var url=image.getAttribute('src');
myWindow=window.open('','Image','width='+newWidth+',height='+newHeight+',resizable=1');
myWindow.document.write('<img src="'+url+'" width="'+newWidth+'" height="'+newHeight+'" />');
}
</script>
<img src="slika1.jpg" onClick="swipe(this);"/>
<img src="slika2.jpg" onClick="swipe(this);"/>
<img src="slika3.jpg" onClick="swipe(this);"/>
To answer a few questions of the original poster:
The first parameter in the window.open() function here is '' (empty string), which basically creates a blank web page. The return value of this function call is the newly opened web page (which is assigned to the variable myWindow). You then drill down into that window object and call it's document.write() function to actually display the desired HTML (the image). In your original code you were simply opening a window that browsed to the image file (not an HTML page). Since that was the case, there is no way you could have actually set the width or height of the image--you were just setting (or trying to) the width and height of the window. Setting the width and height of the window wasn't even working in your example code because you didn't break the variable out of the string. So in the window.open() function you needed to pass a string in the third parameter that looked like:
width=450px,height=600px,resize=1
But what you were actually passing was:
width=largeImage.style.width,height=largeImage.style.height,resizable=1
The swipe() function we created takes in a single parameter "image". When we call this function from the onClick event inside the img tag we use the keyword "this" to pass a reference of itself. Essentially a copy of the img object that called swipe() is passed in as a parameter. So in the function, image.getAttribute('src') references the "src" attribute of the img object that called it, which you need to display in the opened window.

jCrop (jQuery) sometimes fails to load image/cropper area

I've got a pretty simple problem, but I've become clueless on what is causing the problem. In one of my applications I'm using jCrop as a small add-on to crop images to fit in banners/headers etc. These steps will be taken:
1) Select an image (using CKFinder for this, CKFinder returns the image path to an input field)
2) Click a button to load the image
3) Crop the image
4) Save the image
in about 75% of the cases everything goes according to plan, however the in the other 25% of the cases jCrop fails to load the cropping area and leaves it blank. Here's the jQuery code I'm using:
jQuery('#selectimg').live('click', function(e) {
e.preventDefault();
var newsrc = jQuery('#img2').val();
jQuery('#cropbox').attr('src', newsrc);
var jcrop_api = jQuery.Jcrop('#cropbox', {
boxWidth: 700,
boxHeight: 700,
onSelect: updateCoords,
onChange: updateCoords
});
//Some other JS code come's here for buttons (they work all the time)
});
I noticed that when I left the part away where #cropbox is being transformd in a cropable area, that the image is loading just fine, so the mistake lies with the var = jcrop_api part, but I slowsly start to think that there is no solution for this...
This is what I've tried so far:
Making a div <div id="cropper-box"></div> and use jQuery('#cropper-box').append('<img src="" id="cropbox" />'); and afterwards set the value. I tried the same thing but setting the image src in 1 step instead of afterwards.
I tried to put a placeholder on the page <img src="placeholder.png" id="cropbox" /> and change the source upon clicking the button. This works, but the cropperarea stays the size of the image (300x180px or something) and doesn't get bigger as it should.
// Edit:
Trying some more showed me that the image source is being replaced properly(! using Firefox to show the source for the selected text), I double checked the URL but this was a correct URL and a working image.
At the place where the cropper should be, there's an about 10x10 pixel white spot where the cropper icon (a plus sign) is popping up.. but as said before: the image isn't shown.
// Edit 2:
So I've took the sources for both the 1st and the 2nd try for the same image. As told before the first try the image won't load properly and the 2nd try it does (only when the 2nd try is the same image(!!)).
The selected page source shows 1 difference which is, first try:
<img style="position: absolute; width: 0px; height: 0px;" src="http://95.142.175.17/uploads/files/Desert.jpg">
second try:
<img style="position: absolute; width: 700px; height: 525px;" src="http://95.142.175.17/uploads/files/Desert.jpg">
I guess this is the image that's being replace by jCrop, but it's a complete riddle why it puts 0 heigth/width in there the first and the proper sizes the second time.
Okay guys, in case anyone else runs into this problem:
jCrop kinda gets messed up if the actions of loading an image and applying jCrop to it are queued too fast after eachother. I still find it strange that a second attempt works perfect, but I think that has something to do with cached image dimensions which are recognized by the DOM of the page or something.
The solution I came up with was by creating a function that converts the #cropbox into a jCrop area and then setting a 2 second interval, just to give jCrop some time to recognize the image and it's dimensions and then convert the element.
This is the part of html I used (with a preloader):
<div id="cropper-loading" style="display: none;"><img src="images/analytics/ajax-loader.gif" /></div>
<img id="cropbox" src="images/placeholder.png" style="display: none;" />
As you can see both the cropbox image and cropper-loading div are hidden as they are not needed instantly. You could display the placeholder if you wanted though.. Then this HTML form is used:
<input name="image2" id="img2" type="text" readonly="readonly" onclick="openKCFinder(this)" value="click here to select an image" style="width: 285px;" /> <button class="button button-blue" type="submit" name="load" id="selectimg">Load Image in cropper</button>
In my case I've been using KCFinder to load the images (it's part of CKEditor, really worth watching into!), KCFinder handles uploads, renaming etc and after choosing it returns the chosen image path (relative/absolute is configurable) to the input field.
Then when clicking #selectimg this code is called:
jQuery('#selectimg').click(function(e) {
e.preventDefault();
jQuery('#cropper-loading').css('display', 'block');
var newsrc = jQuery('#img2').val();
jQuery('#cropbox').attr('src', newsrc);
jQuery('#img').val(newsrc);
function createJcropArea() {
jQuery('#cropper-loading').css('display', 'none');
jQuery('#cropbox').css('display', 'block');
var jcrop_api = jQuery.Jcrop('#cropbox', {
boxWidth: 700,
boxHeight: 700,
onSelect: updateCoords,
onChange: updateCoords
});
clearInterval(interval);
}
var interval = setInterval(createJcropArea, 2000);
});
At first I prevent the link too be followed as it normally would (or button action) and after that the loading div is displayed (that's my reason for hiding the placeholder image, otherwise it would look messed up).
Then the image location is being loaded from the input field and copied into another (#img), this field is used to process the image afterwards (PHP uses the value of #img to load this image). Also simultaneously the #cropbox src is being set to the new image.
And here comes the part which solved my problem:
Instead of directly activating jCrop, I've made a function that:
1) hides the loading icon
2) displays the image
3) converts #cropbox into a jCrop area
4) clean the interval (otherwise it would loop un-ending)
And after this function you can see that, just to be save, I took 2 seconds delay before the jCrop area is being converted.
Hope it helps anyone in the future!
Cheers and thanks for thinking #vector and whoever else did ;-)
Creating an 'Image' object and setting up the 'src' attribute does not apply that you can treat the image like it had already been loaded.
Also, giving any fixed timeout interval does not guaranty the image has already been loaded.
Instead, you should set up an 'onload' callback for the Image Object - which will then initialize the Jcrop Object:
var src = 'https://example.com/imgs/someimgtocrop.jpg';
var tmpImg = new Image();
tmpImg.onload = function() {
//This is where you can safely create an image and a Jcrop Object
};
tmpImg.src = src; //Note that the 'src' attribute is only added to the Image Object after the 'onload' listener was defined
Try the edge library on the repo here: https://github.com/tapmodo/Jcrop
This should solve your problem. The lines that are changed to solve your problem:
// Fix size of crop image.
// Necessary when crop image is within a hidden element when page is loaded.
if ($origimg[0].width != 0 && $origimg[0].height != 0) {
// Obtain dimensions from contained img element.
$origimg.width($origimg[0].width);
$origimg.height($origimg[0].height);
} else {
// Obtain dimensions from temporary image in case the original is not loaded yet (e.g. IE 7.0).
var tempImage = new Image();
tempImage.src = $origimg[0].src;
$origimg.width(tempImage.width);
$origimg.height(tempImage.height);
}
Don't call this function onChange : updateCoords
Try it without and it will run smooth on mobiles.
You can create base64 directly and show them as an image wherever you want.
Here my weird but fantastic solution:
if (obj.tagName == 'IMG') {
var tempImage = new Image();
tempImage.src = $origimg[0].src;
$origimg.width(tempImage.width);
$origimg.height(tempImage.height);
if ($origimg[0].width > 1 && $origimg[0].height > 1) {
$origimg.width($origimg[0].width);
$origimg.height($origimg[0].height);
} else {
var tempImage = new Image();
tempImage.src = $origimg[0].src;
$origimg.width(tempImage.width);
$origimg.height(tempImage.height);
//console.log('error'+$origimg[0].width + $origimg[0].height);
}
I know this is old, but it was happening randomly to my install recently. Found that it was due to images not being full loaded before before jCrop intialized.
All it took to fix it was wrapping the jCrop initialization stuff inside of a
$(window).on("load", function () { //jcrop stuff here });
And it has been working well since.

How to show a spinner while loading an image via JavaScript

I'm currently working on a web application which has a page which displays a single chart (a .png image). On another part of this page there are a set of links which, when clicked, the entire page reloads and looks exactly the same as before except for the chart in the middle of the page.
What I want to do is when a link is clicked on a page just the chart on the page is changed. This will speed things up tremendously as the page is roughly 100kb large, and don't really want to reload the entire page just to display this.
I've been doing this via JavaScript, which works so far, using the following code
document.getElementById('chart').src = '/charts/10.png';
The problem is that when the user clicks on the link, it may take a couple of seconds before the chart changes. This makes the user think that their click hasn't done anything, or that the system is slow to respond.
What I want to happen is display a spinner / throbber / status indicator, in place of where the image is while it is loading, so when the user clicks the link they know at least the system has taken their input and is doing something about it.
I've tried a few suggestions, even using a psudo time out to show a spinner, and then flick back to the image.
A good suggestion I've had is to use the following
<img src="/charts/10.png" lowsrc="/spinner.gif"/>
Which would be ideal, except the spinner is significantly smaller than the chart which is being displayed.
Any other ideas?
I've used something like this to preload an image and then automatically call back to my javascript when the image is finished loading. You want to check complete before you setup the callback because the image may already be cached and it may not call your callback.
function PreloadImage(imgSrc, callback){
var objImagePreloader = new Image();
objImagePreloader.src = imgSrc;
if(objImagePreloader.complete){
callback();
objImagePreloader.onload=function(){};
}
else{
objImagePreloader.onload = function() {
callback();
// clear onLoad, IE behaves irratically with animated gifs otherwise
objImagePreloader.onload=function(){};
}
}
}
You could show a static image that gives the optical illusion of a spinny-wheel, like these.
Using the load() method of jQuery, it is easily possible to do something as soon as an image is loaded:
$('img.example').load(function() {
$('#spinner').fadeOut();
});
See: http://api.jquery.com/load-event/
Use the power of the setTimeout() function (More info) - this allows you set a timer to trigger a function call in the future, and calling it won't block execution of the current / other functions (async.).
Position a div containing the spinner above the chart image, with it's css display attribute set to none:
<div> <img src="spinner.gif" id="spinnerImg" style="display: none;" /></div>
The nbsp stop the div collapsing when the spinner is hidden. Without it, when you toggle display of the spinner, your layout will "twitch"
function chartOnClick() {
//How long to show the spinner for in ms (eg 3 seconds)
var spinnerShowTime = 3000
//Show the spinner
document.getElementById('spinnerImg').style.display = "";
//Change the chart src
document.getElementById('chart').src = '/charts/10.png';
//Set the timeout on the spinner
setTimeout("hideSpinner()", spinnerShowTime);
}
function hideSpinner() {
document.getElementById('spinnerImg').style.display = "none";
}
Use CSS to set the loading animation as a centered background-image for the image's container.
Then when loading the new large image, first set the src to a preloaded transparent 1 pixel gif.
e.g.
document.getElementById('mainimg').src = '/images/1pix.gif';
document.getElementById('mainimg').src = '/images/large_image.jpg';
While the large_image.jpg is loading, the background will show through the 1pix transparent gif.
Building on Ed's answer, I would prefer to see something like:
function PreLoadImage( srcURL, callback, errorCallback ) {
var thePic = new Image();
thePic.onload = function() {
callback();
thePic.onload = function(){};
}
thePic.onerror = function() {
errorCallback();
}
thePic.src = srcURL;
}
Your callback can display the image in its proper place and dispose/hide of a spinner, and the errorCallback prevents your page from "beachballing". All event driven, no timers or polling, plus you don't have to add the additional if statements to check if the image completed loading while you where setting up your events - since they're set up beforehand they'll trigger regardless of how quickly the images loads.
Some time ago I have written a jQuery plugin which handles displaying a spinner automatically http://denysonique.github.com/imgPreload/
Looking in to its source code should help you with detecting when to display the spinner and with displaying it in the centre of the loaded image.
I like #duddle's jquery method but find that load() isn't always called (such as when the image is retrieved from cache in IE). I use this version instead:
$('img.example').one('load', function() {
$('#spinner').remove();
}).each(function() {
if(this.complete) {
$(this).trigger('load');
}
});
This calls load at most one time and immediately if it's already completed loading.
put the spinner in a div the same size as the chart, you know the height and width so you can use relative positioning to center it correctly.
Aside from the lowsrc option, I've also used a background-image on the img's container.
Be aware that the callback function is also called if the image src doesn't exist (http 404 error). To avoid this you can check the width of the image, like:
if(this.width == 0) return false;
#iAn's solution looks good to me. The only thing I'd change is instead of using setTimeout, I'd try and hook into the images 'Load' event. This way, if the image takes longer than 3 seconds to download, you'll still get the spinner.
On the other hand, if it takes less time to download, you'll get the spinner for less than 3 seconds.
I would add some random digits to avoid the browser cache.

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