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Why does onload cause my image switch to flicker?

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"/>

Why is this java script not working?

In reference to this post: How to display loading image while actual image is downloading
I have the following code, but for some reason I cannot get the #loader_img to hide. I would also like to add a preloader because the large image is really heavy, but I want to keep it simple if possible since I am new to javascript...
<img id="loader_img" src="img/ajax-loader.gif" alt="Loading..." />
<div class="magnifier" style="height: 584px; width: 467px; margin: 20px;">
<div class="maglens">
<img id="imgload" src="img/largeimage.jpg" />
</div>
</div>
JS:
// show loading image
$("#loader_img").show();
$("#imgload").hide();
// main image loaded ?
$("#imgload").on('load', function(){
// hide/remove the loading image
$("#loader_img").hide();
});
Any help will be much appreciated! Thank you!

The image's load event is almost certainly firing before you hook the event. Since it's already fired when you hook the event, you never see it occur.
Also, you start out hiding the image (#imgload), but you never then show it.
To ensure that you get the event, you have to hook load before setting the image's src.
Alternately, you can use the image's complete property to know if it's already been loaded:
// show loading image
$("#loader_img").show();
$("#imgload").hide();
// main image loaded ?
var img = $("#imgload");
if (img[0].complete) {
imageDone();
} else {
img.on('load', imageDone);
}
function imageDone() {
// hide/remove the loading image
$("#loader_img").hide();
// And show the image!
img.show();
}
You also have to ensure that the code above runs after the elements have been created. The best way to do that is to put your script tag containing the code after the elements it refers to in the HTML (usually putting it just before the closing </body> tag works well). As a second-best solution, you can use jQuery's ready function. Either way, you'll still need to handle the possibility the load event has already fired.
Here's an example:
<div id="loader_img">Loading</div>
<div class="content">
<img id="imgload" src="http://i.stack.imgur.com/rTQCa.jpg?s=512&g=1" />
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script>
(function() { // Avoid creating globals
// show loading image
$("#loader_img").show();
$("#imgload").hide();
// main image loaded ?
var img = $("#imgload");
if (img[0].complete) {
console.log("Complete");
imageDone();
} else {
console.log("Wait for load");
img.on('load', imageDone);
}
function imageDone() {
console.log("Loaded");
// hide/remove the loading image
$("#loader_img").fadeOut();
// And show the image!
img.show();
}
})();
</script>

Hi you may use this method. jQuery.ready()I have tried on my computer and it's okay this way.
BTW, you forgot to let the "imgload" show again.
// show loading image
$("#loader_img").show();
$("#imgload").hide();
// main image loaded ?
$("#imgload").ready(function(){
// hide/remove the loading image
$("#loader_img").hide();
$("#imgload").show(); // show the loaded img again
});

I think that the script is executed before the DOM is loaded.
Take your script and put it between:
$(function () {
//Your code here
});
This will insure that the code will run after the DOM is loaded.

check if multiple images loaded within certain timeinterval; if not then replace with other url

Problem- I am displaying some images on a page which are being served by some proxy server. In each page I am displaying 30 images ( 6 rows - 5 in each row). Here if due to overload or due to any other issue if proxy server could not able to server images( either all images or some of them) in 6 seconds then I want to replace unloaded image url with some other url using javascript so that I could display 30 images at the end.
What I tried is below.
objImg = new Image();
objImg.src = 'http://www.menucool.com/slider/prod/image-slider-4.jpg';
if(!objImg.complete)
{
alert('image not loaded');
}else{
img.src = 'http://www.menucool.com/slider/prod/image-slider-4.jpg';
}
I also tried with below code.
$('img[id^="picThumbImg_"]').each(function(){
if($(this).load()) {
//it will display loaded image id's to console
window.console.log($(this).attr('id'));
}
});
I could not use set time-out for each image because it will delay all page load.
I checked other similar question on stack-overflow but no solution worked me perfectly as I need to display multiple images.Please guide how to proceed.

You don't have to wait 6 seconds, or using TimeOut. You can check if the images are loaded or not using the onload Javascript/Jquery event. I know, it will take a little bit to dispatch the onerror event, let see:
Why don't use the load Jquery event on the window or the image itself?
$(window).load(function(){
//check each image
})
Disadvantage:
It will wait for other resources like scripts, stylesheets & flash, and not just images, which may or may not be OK to you.
If the image loads from the cache, some browsers may not fire off the event (included yours and that's why your code is not working)
Why don't use the error Jquery event on the image itself?
$('img[id^="picThumbImg_"]').error(function(){
//image loading error
})
Disadvantages:
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
Note:: Error is almost the same that the load event
Improving the code!:
$('img[id^="picThumbImg_"]').one('error', function() {
// image load error
}).each(function() {
if(!this.complete) $(this).error();
});
This will avoid few things of the previous code, but you still will have to wait if it's a 404 and you're replacing it in the onerror event, that will take a little bit right?
So, what now!
You can use this awesome plugin!. Once you add the reference, you just have to use something like:
var imgLoad = imagesLoaded('#img-container');
imgLoad.on( 'always', function() {
// detect which image is broken
for ( var i = 0, len = imgLoad.images.length; i < len; i++ ) {
if(!imgLoad.images[i].isLoaded){
//changing the src
imgLoad.images[i].img.src = imgLoad.images[i].img.getAttribute("data-src2");
}
}
});
Your HTML markup should look like:
<div id="img-container">
<div class="row">
...
</div>
<div class="row">
<img src="original-path.jpg" data-src2="alternative-path.jpg">
...
</div>
<div class="row">
...
</div>
</div>
Note: You don't need jQuery in this case and this plugin is suggested by Paul Irish ;)

Give all your images a specific class. Loop through your images and use .load() to check if loaded, example below...
Detect image load

How do I abort image <img> load requests without using window.stop()

I have a very long page that dynamically loads images as users scroll through.
However, if a user quickly scrolls away from a certain part of the page, I don't want the images to continue loading in that now out-of-view part of the page.
There are lots of other requests happening on the page simultaneously apart from image loading, so a blunt window.stop() firing on the scroll event is not acceptable.
I have tried removing & clearing the img src attributes for images that are no longer in view, however, since the request was already started, the image continues to load.
Remember that the image src was filled in as the user briefly scrolled past that part of the page. Once past though, I couldn't get that image from stop loading without using window.stop(). Clearing src didn't work. (Chrome & FF)
Similar posts I found that get close, but don't seem to solve this problem:
Stop loading of images with javascript (lazyload)?
Javascript: Cancel/Stop Image Requests
How to cancel an image from loading

What you are trying to do is the wrong approach, as mentioned by nrabinowitz. You can't just "cancel" the loading process of an image (setting the src attribute to an empty string is not a good idea). In fact, even if you could, doing so would only make things worst, as your server would continually send data that would get cancelled, increasing it's load factor and slow it down. Also, consider this:
if your user scroll frenetically up and down the page, he/she will expect some loading delays.
having a timeout delay (ex: 200 ms) before starting to load a portion of the page is pretty acceptable, and how many times will one stop and jump after 200 ms interval on your page? Even it it happens, it comes back to point 1
how big are your images? Even a slow server can serve about a few tens of 3Kb thunbnails per second. If your site has bigger images, consider using low and hi resolution images with some components like lightBox
Often, computer problems are simply design problems.
** EDIT **
Here's an idea :
your page should display DIV containers with the width and height of the expected image size (use CSS to style). Inside of each DIV, add an link. For example :
<div class="img-wrapper thumbnail">
Loading...
</div>
Add this Javascript (untested, the idea is self describing)
$(function() {
var imgStack;
var loadTimeout;
$(window).scroll(function() {
imgStack = null;
if (loadTimeout) clearTimeout(loadTimeout);
loadTimeout = setTimeout(function() {
// get all links visible in the view port
// should be an array or jQuery object
imgStack = ...
loadNextImage();
}, 200); // 200 ms delay
});
function loadNextImage() {
if (imgStack && imgStack.length) {
var nextLink = $(imgStack.pop()); // get next image element
$('<img />').attr('src', nextLink.attr('href'))
.appendTo(nextLink.parent())
.load(function() {
loadNextImage();
});
// remove link from container (so we don't precess it twice)
nextLink.remove();
}
};
});

Well, my idea:
1) initiate an AJAX request for the image, if it succeeds, the image goes to the browser cache, and once you set the 'src' attribute, the image is shown from the cache
2) you can abort the XHR
I wrote a tiny server with express emulating the huge image download (it actually just waits 20 seconds, then returns an image). Then I have this in my HTML:
<!DOCTYPE html>
<html>
<head>
<style>
img {
width: 469px;
height: 428px;
background-color: #CCC;
border: 1px solid #999;
}
</style>
</head>
<body>
<img data-src="./img" src="" />
<br />
<a id="cancel" href="javascript:void(0)">CANCEL</a>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script>
$(function () {
var xhr, img = $('img'), src = img.data('src');
xhr = $.ajax(src, {
success: function (data) { img.attr('src', src) }
});
$('#cancel').click(function (){
xhr.abort();
})
});
</script>
</body>
</html>

You can load your images using ajax calls, and in case that the uses scrolls-out, you can abort the calls.
In jQuery pseudo-code it would be something like that (forgive me mistakes in syntax, it is just an example):
1) tag images that you want to load
$(".image").each( function(){
if ( is_in_visible_area(this) ) { // check [1] for example
$(this).addClass("load_me");
} else {
$(this).addClass("dont_load");
}
});
2) load images
ajax_requests = {};
$(".image.load_me").each( function(){
// load image
var a = $.ajax({
url: 'give_me_photos.php',
data: {img: photo_id},
success: function(html){
photo_by_id(photo_id), img.append(html);
}
});
ajax_requests[photo_id] = a;
});
3) cancel loading those out of the screen
for( id in ajax_requests ) {
if ( ! is_in_visible_area(id) ) {
ajax_requests[id].abort();
}
}
Of course, add also some checking if the image is already loaded (e.g. class "loaded")
[1]. Check if element is visible after scrolling
[2]. Abort Ajax requests using jQuery

BTW, another idea that might work:
1) create a new iframe
2) inside of the iframe have the script that starts loading the image, and once it's loaded, call the .parent's method
3) when in need, stop the iframe content loading using .stop on the iframe object

Use a stack to manage ajax requests (means you will have serial loading instead of parallel but it is worth it)
On scroll stop, wait for 300ms and then push all images inside view-area into stack
Every time a user scrolls check if a stack is running. (fyi - you can stop all requests to a particular url instead of killing all ajax calls. also you can use regex so it should not stop any other requests on the page)
If an existing stack is running - pop all the images that are in it except for the top most one.
On all ajax calls - bind beforeSend() event to remove that particular image from the stack
It is late right now, but we have done something very similar at work - if you need the detailed code let me know.
Cheers!

Maybe you could serve the image through a php script which would check a field in the the db (or better yet a memcached) that would indicate stop loading. the script would portion up the image into chunks and pause in between each chunk and check if the stop flag for the particular request is. If it is set you send the header with A 204 no content which as soon as the browser gets it will stop receiving.
This may be a bit over kill though.

The solution could be a webworker. a webworker can be terminated and with him the connection.
But there is a small problem that the webworker uses the limited connections of the browser so the application will be blocked.
Right now I'm working on a solution with serviceWorkers - they don't have a connection limit (I hope so)

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.