Develop Reference

Function firing before images has finished loading

I'm trying to get a pre loader screen to work but am hitting a roadblock.
My goal: To have the loading animation/divs dissapear when the image has finished loading.
I've tried to accomplish this with a simple .ready function and still the function that removes the loading animation fires white the image is still loading and the viewer will see the image load in real time.
$("#defaultImage").ready(function(){
TweenMax.to(["#backgroundLoad","#loadBoxes"],1,{alpha:0,delay:0.75});
console.log('Page has loaded');
});
Is this incorrect? I thought that this will wait for the entire page(images included) to load and then fire the function inside it.
I've tried the below too and it doesn't seem to fire the console.log at all
document.getElementById("defaultImage").onload = function (){
console.log('Page has loaded');
};
Pen in question below. You can see the issue if you view it in debug view and do a hard refresh.
http://codepen.io/mhcreative/pen/GoxLPo?editors=0011
Any help would be much appreciated.
Thanks, All.

Here try this if you still want it natively.
$(document).ready(function(){
var img = new Image(); // Create new img element
img.addEventListener("load", function() {
TweenMax.to(["#backgroundLoad","#loadBoxes"],1,{alpha:0,delay:0.75});
}, false);
img.src = 'src/to/img'; // Set source path
$("#defaultImage").append(img); //append loaded image inside div
});

Using JavaScript to dynamically change display style in img tags

I show links to 240 images on a page. The real images are uploaded by users. I tried to avoid showing an empty image if users did not upload it yet. jQuery did not work for me because of conflicts, so I have to do it in pure JavaScript.
image(s) links:
<img class="photo240" src="http://www.example.com/i/%%GLOBAL__AuthorID%%/p/b01.jpg" onerror="imgError()">
My JavaScript:
function imgError()
{
alert('The image could not be loaded.');
var _aryElm=document.getElementsByTagName('img'); //return an array with every <img> of the page
for( x in _aryElm) {
_elm=_aryElm[x];
_elm.className="photo240off";
}
}
The style photo240off equals to display:none.
Right now, whenever an image misses, all the images are turned to style photo240off and I want only the missing image to be hidden. So there is something wrong with my script.
(the overall script works well, because I get the alert).

Use this to get the image with the error.
Change to:
onerror="imgError(this)"
Then the function can be:
function imgError(el) {
alert('The image could not be loaded.');
el.className = "photo240off";
}

You need to reference the image from your onerror call and change the class only for that one.
Something like this:
HTML
<img class="photo240" src="example.jpg" onerror="imgError(this)">
JS
function imgError(el) {
el.className="photo240off";
}

Finding height of image using JavaScript - image load error

I can't seem to find the height of an image using Javascript on a Typo3 website.
Basically I have javascript that runs inside a $(document).ready(function () { .
It looks for an image on the page and finds its height & width, then carries out opperations based on the results.
Sometimes this works and sometimes it doesn't. Usually, I get a width value but no height. I suspect this is because the browser hasn't finnished loading the image.
To solve this I have included a 2second delay to ensure img is loaded before looking for its height. But that isn't a very good way of solving the problem, especially if someone has low download speeds.
How else could I check that an image is loaded fully before carrying out opperations?
Here is some HTML:
<div class="resize-thumb-img">
<img src="#.jpg" />
</div>
<div class="resize-thumb-img">
<img src="#.jpg" />
</div>
<div class="resize-thumb-img">
<img src="#.jpg" />
</div>
And some JS:
$(document).ready(function () {
setTimeout(myFunctionX, 2000);
function myFunctionX() {
$(".resize-thumb-img img").each(function(){ //for each image
console.log("working on image: "+$(this).width() +"x"+$(this).height());
/* MORE WORK HERE */
});
}
});
The console log can give results like 235x420 OR 235x0 OR 0x0

I found a solution which I think helps in this context. It checks an image to see if its width is "0". If it is, it waits 1 second and then tries again. If its not "0", it calls the function I had before. Might be useful to include || null to the first if statement - I havn't tested on all browsers.
$(document).ready(function () {
checkLoadState();
function checkLoadState() //checks to see if images are loaded before continuing
{
if ($(".resize-thumb-img img").width() != "0")
{
console.log("Images loaded. Resizig...");
myFunctionX();
}
else
{
console.log("Waiting for images to load.");
setTimeout(checkLoadState, 1000); // check again in a second
}
}
function myFunctionX() {
$(".resize-thumb-img img").each(function(){ //for each image
console.log("working on image: "+$(this).width() +"x"+$(this).height());
/* MORE WORK HERE */
});
}
});

You can try the below one:
$('img').each(function() {
$(this).attr('height',$(this).height());
$(this).attr('width',$(this).width());
});
This will help you to find the height of your image using jquery.

If you have control over the server-side scripts, couldn't you simply store the size of the bitmap in a database together with its filename? Then you could set the WIDTH and HEIGHT attributes of the IMG elements.

What you need to do is bind a function to the load event for any images that aren't yet loaded, something like this
function processImage(imageElement){
// do your stuff here
var img=$(imageElement);
console.log("working on image: "+img.width() +"x"+img.height());
}
$(document).ready(function () {
// iterate through the images
$(".resize-thumb-img img").each(function(){
var img = $(this);
if(img.width()==0 || img.height()==0){
// image has not fully loaded yet, so process it once loaded
img.on('load',function(){processImage(this);})
}else{
// image is loaded so process the image straight away
processImage(this);
}
})
})

Placeholder while an image is loading with Ember.js [duplicate]

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.

Pre Load images to display later on click event jQuery

I have a web page where lots of images called from server using image
scr attribute.
I have created a function like which is triggered by td click.
function GoToStep(stepNo) {
var imgSrc = $("#h1" + stepNo).val();
$(".img_vertical").css("background-image", "url(" + imgSrc + ")");
}
Now the problem is this. For slower connections the images come after some
moment.
Can I pre load images to avoid waiting time when user clicks
td?
I have seen some jquery function to pre load images.
Kindly give some idea how can I achieve it.

Pre-loading an image is equivalent to loading an image but never displaying it. So, you can easily do it like this:
<img src="image.png" alt="" style="display:none;"/>
Now this image will be loaded as soon as the html starts rendering. Whenever you need to use this image as a display or background, just set the address to image.png and it will automatically be fetched from browser's cache.

This can be done using some javascript functions. Quoting from another question.
function preload(arrayOfImages) {
$(arrayOfImages).each(function(){
$('<img/>')[0].src = this;
// Alternatively you could use:
// (new Image()).src = this;
});
}
// Usage:
preload([
'img/imageName.jpg',
'img/anotherOne.jpg',
'img/blahblahblah.jpg'
]);
Explanation of how javascript preloaders work (different question)
[...] The way it works is simply by creating a new Image object and setting
the src of it, the browser is going to go grab the image. We're not
adding this particular image to the browser, but when the time comes
to show the image in the page via whatever method we have setup, the
browser will already have it in its cache and will not go fetch it
again. [...]
So in your case, you should use something like
$(function() {
// Do stuff when DOM is ready
preload([
'img/bg1.jpg',
'img/bg2.jpg',
'img/bg3.jpg'
]);
});