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OnClick loading background-image from url with timeout or fail function?

I have an HTML button with an onclick function "clicked()".
If clicked I want to load an image as "background-image" of a div tag.
The image shall be loaded from a server that serves the image very unreliable (rain-radar),
very high answer time up to timeout. I have no control of the server but I am allowed
to fetch the image.
If the image cannot be loaded or is not loaded after 30 seconds I want to show either a failover image or a simple text message to try again later.
I tried to define a second (failover) image url to the style background-image attribute but
then my page always loads the failover image and I guess that's not how it works. Also I dont want to show a "loading image failed" image while page still waits to receive an answer...
index.html
...
GoToDiv
...
javascript:
function clicked(){
document.getElementById('gotoDiv').style.backgroundImage = "url('https://UNRELIABLE.SERVER/pic.jpg'), url('/failover.jpg')";
}
I there a proper way to do that?

You can try a preloading technique
function clicked() {
var elem = document.getElementById('gotoDiv');
elem.style.backgroundImage = 'url("loading.gif")';
function setErrorImg () {
elem.style.backgroundImage = 'url("failover.jpg")';
}
var timer = window.setTimeout(setErrorImg, 30000);
var img = new Image();
img.onload = function() {
window.clearTimeout(timer);
elem.style.backgroundImage = 'url("' + img.src + '")';
};
img.onerror = setErrorImg;
img.src = 'https://UNRELIABLE.SERVER/pic.jpg';
}

Execute js after all image loaded not working

(not duplicate, because not find exactly/easy solution)
I'm trying to execute JS after all images completely loaded. My goal is, when all images finish load completely, then removeClass my-loader and addClass visible to main-slider div.
HTML:
<div class='main-slider my-loader'>
<img src="https://unsplash.it/200/300/">
<img src="https://unsplash.it/200/300/">
<img src="https://unsplash.it/200/300/">
</div>
Execute below js when all images completely loaded
$(".main-slider").removeClass("my-loader").addClass("visible");
Tried this js :
But not works properly on my site, problem is when i clear browser cache, then it works/execute! when i reload page then next time it's not works/execute! It only works when i clear browser cache.
var img = $('.main-slider img')
var count = 0
img.each(function(){
$(this).load(function(){
count = count + 1
if(count === img.length) {
$('.main-slider').removeClass('my-loader').addClass('visible')
}
});
});
Any simple solution? Thanks in advance.

jQuery provides a way to register a callback for the window load event which will fire when the entire page, including images and iframes, are loaded.
Reference: https://learn.jquery.com/using-jquery-core/document-ready/
Your code should look something like:
$( window ).load(function () {
var img = $('.main-slider img')
var count = 0
img.each(function(){
$(this).load(function(){
count = count + 1
if(count === img.length) {
$('.main-slider').removeClass('my-loader').addClass('visible')
}
});
});
});

Here's how to do this, using Deferreds and native handlers, and calling the onload handler if the image is cached in older browsers etc.
var img = $('.main-slider img');
var defs = img.map(function(){
var def = new Deferred();
this.onload = def.resolve;
this.onerror = def.reject;
if (this.complete) this.onload();
return def.promise();
});
$.when.apply($, defs).then(function() {
$('.main-slider').removeClass('my-loader').addClass('visible')
});

Something goes wrong with fadeIn

Hello I want to fadeOut image, and then do fadeIn with a new one, so I wrote a simple code, but something goes wrong, because when .photo img fadesOut, then fadesIn this same photo, but after, a few second its changes because of new "src", but even if browser didn't load a new image, the old one shound't show, becuase src is changed, but it shows, and after a second, maybe two changes to the new one. Can somebody tell me what's wrong?
var dimage = $next.children("img").attr("rel");
$(".photo img").fadeOut("slow", function () {
$(".photo img").attr("src", dimage);
$(".photo img").fadeIn("slow");
});

This may be because the image has to load after the src is altered.
Consider putting the image in a tag, then setting the css property to display:none. This way the image will preload in the browser before your script runs and will be available when it does.

you aren't giving the new image enough time to load.
function loadImage (src) {
return $.Deferred(function(def){
var img = new Image();
img.onload = function(){
def.resolve(src);
}
img.src = src;
}).promise();
}
var dimage = $next.children("img").attr("rel");
var imageLoadedDef = loadImage(dimage);
$(".photo img").fadeOut("slow", function () {
def.done(function(src){
$(".photo img").attr("src", src);
$(".photo img").fadeIn("slow");
});
});

the problem as highlighted is about images not ready for display when you call them, so the solution is to preload them before starting the slideshow, create a function with an array of images path
function preLoad(){
var imgs = {'test1.jpg', 'test2.jpg', 'test3.jpg'};
var img = document.createElement('img');
for(var i = 0; i < imgs.leght; i++){
img.src = imgs[i]; //all images gets preloaded at this stage
}
startSlider(); //here you will do your code
}

Why does this "loading message" script not work in FF?(javascript)

I have this script which should show the text "Loading..." while images are loading, then change the text to "loaded" when all images are loaded. I added a button to load new images to make sure that it works for dynamically loaded images as well.
This works perfectly in Chrome but in Firefox the "Loading..." text never appears. I have no idea why this would be. The page begins loading and not all images are loaded so it should create the text "Loading.." but it doesn't. Then when all images are done loading the text "Loading" appears.
I just don't get why one message would appear and the other wouldn't. Especially because there are no qualifications that have to be met before creating the "Loading..." text, it should just fire automatically.
jsfiddle Example | Full Page Example
$(document).ready(function() {
var checkComplete = function() {
if($('img').filter(function() {return $('img').prop('complete');}).length == $('img').length) {
$('.status').text('Loaded');
} else {
$('.status').text('Loading...');
}
};
$('img').on('load',function() {
checkComplete();
});
$('#button').click(function() {
$('img.a').attr('src' , 'http://farm9.staticflickr.com/8545/8675107979_ee12611e6e_o.jpg');
$('img.b').attr( 'src' , 'http://farm9.staticflickr.com/8382/8677371836_651f586c99_o.jpg');
checkComplete();
});
checkComplete();
});

You have several issues in the code.
First off, the checkComplete() function is not written correctly. It should be this:
var checkComplete = function() {
var imgs = $('img');
if(imgs.filter(function() {return this.complete;}).length == imgs.length) {
$('.status').text('Loaded');
} else {
$('.status').text('Loading...');
}
};
The main fix here is that the filter callback needs to refer to this.complete, not to $('img').prop('complete') because you are trying to filter a single item at a time.
Second off, you are relying on both .complete and .load working correctly AFTER you've changed the .src value. This is explicitly one of the cases where they do not work properly in all browsers.
The bulletproof way to work around this is to create a new image object for the new images, set the onload handler before you set the .src value and when both onload handlers have fired, you will know that both new images are loaded and you can replace the once you have in the DOM with the new ones.
Here is a version that works in FF:
$(document).ready(function() {
$('#button').click(function() {
var imgA = new Image();
var imgB = new Image();
imgA.className = "a";
imgB.className = "b";
var loaded = 0;
imgA.onload = imgB.onload = function() {
++loaded;
if (loaded == 2) {
$("img.a").replaceWith(imgA);
$("img.b").replaceWith(imgB);
$('.status').text('Loaded');
}
}
// the part with adding now to the end of the URL here is just for testing purposes to break the cache
// remove that part for deployment
var now = new Date().getTime();
imgA.src = 'http://farm9.staticflickr.com/8545/8675107979_ee12611e6e_o.jpg?' + now;
imgB.src = 'http://farm9.staticflickr.com/8382/8677371836_651f586c99_o.jpg?' + now;
$('.status').text('Loading...');
});
});
Working demo: http://jsfiddle.net/jfriend00/yy7GX/
If you want to preserve the original objects, you can use the newly created objects only for preloading the new images and then change .src after they've been preloaded like this:
$(document).ready(function() {
$('#button').click(function() {
var imgA = new Image();
var imgB = new Image();
var loaded = 0;
imgA.onload = imgB.onload = function() {
++loaded;
if (loaded == 2) {
$("img.a")[0].src = imgA.src;
$("img.b")[0].src = imgB.src;
$('.status').text('Loaded');
}
}
// the part with adding now to the end of the URL here is just for testing purposes to break the cache
// remove that part for deployment
var now = new Date().getTime();
imgA.src = 'http://farm9.staticflickr.com/8545/8675107979_ee12611e6e_o.jpg?' + now;
imgB.src = 'http://farm9.staticflickr.com/8382/8677371836_651f586c99_o.jpg?' + now;
$('.status').text('Loading...');
});
});
Working demo of this version: http://jsfiddle.net/jfriend00/ChSQ5/

From the jQuery API .load method
Caveats of the load event when used with images
A common challenge developers attempt to solve using the `.load()` shortcut is to execute a function when an image (or collection of images) have completely loaded. There are several known caveats with this that should be noted. These are:
It doesn't work consistently nor reliably cross-browser
It doesn't fire correctly in WebKit if the image src is set to the same src as before
It doesn't correctly bubble up the DOM tree
Can cease to fire for images that already live in the browser's cache

javascript preloader/progress/percentage

I'm having trouble finding any good information on how to make a javascript(or jquery) progress bar WITH text that tells you the percentage.
I don't want a plug in, I just want to know how it works so that I can adapt it to what I need. How do you preload images and get a variable for the number of images that are preloaded. Also, how do you change html/css and-or call a function, based on the number of images that are loaded already?

<img> elements have an onload event that fires once the image has fully loaded. Therefore, in js you can keep track of the number of images that have loaded vs the number remaining using this event.
Images also have corresponding onerror and onabort events that fire when the image fails to load or the download have been aborted (by the user pressing the 'x' button). You also need to keep track of them along with the onload event to keep track of image loading properly.
Additional answer:
A simple example in pure js:
var img_to_load = [ '/img/1.jpg', '/img/2.jpg' ];
var loaded_images = 0;
for (var i=0; i<img_to_load.length; i++) {
var img = document.createElement('img');
img.src = img_to_load[i];
img.style.display = 'hidden'; // don't display preloaded images
img.onload = function () {
loaded_images ++;
if (loaded_images == img_to_load.length) {
alert('done loading images');
}
else {
alert((100*loaded_images/img_to_load.length) + '% loaded');
}
}
document.body.appendChild(img);
}
The example above doesn't handle onerror or onabort for clarity but real world code should take care of them as well.

What about using something below:
$('#btnUpload').click(function() {
var bar = document.getElementById('progBar'),
fallback = document.getElementById('downloadProgress'),
loaded = 0;
var load = function() {
loaded += 1;
bar.value = loaded;
/* The below will be visible if the progress tag is not supported */
$(fallback).empty().append("HTML5 progress tag not supported: ");
$('#progUpdate').empty().append(loaded + "% loaded");
if (loaded == 100) {
clearInterval(beginLoad);
$('#progUpdate').empty().append("Upload Complete");
console.log('Load was performed.');
}
};
var beginLoad = setInterval(function() {
load();
}, 50);
});
JSFIDDLE
You might also want to try HTML5 progress element:
<section>
<p>Progress: <progress id="p" max=100><span>0</span>%</progress></p>
<script>
var progressBar = document.getElementById('p');
function updateProgress(newValue) {
progressBar.value = newValue;
progressBar.getElementsByTagName('span')[0].textContent = newValue;
} </script>
</section>
http://www.html5tutorial.info/html5-progress.php