Develop Reference

Image source not changing with JavaScript

Please answer this question, as I am struggling a lot with it.
I am trying to change image source on mouse over. I am able to do it, but image is not displaying on page.
I am trying to change image source to cross domain URL. I can see that in DOM image source is changing but on page its not.
I have tried all solutions mentioned in LINK, but none of them is working.
Please let me solution to problem.
NOTE:
I can see in network tab image is taking some time to download (about 1 sec).
It is an intermediate issue, sometime image is loading and sometimes its not
CODE:
document.getElementsByTagName('img')[0].addEventListener('mouseover', function()
{
document.getElementsByTagName('img')[0].setAttribute('src', 'url/of/the/image');
});

have you tried loading images before everything else?
function initImages(){
var imC = 0;
var imN = 0;
for ( var i in Images ) imN++;
for(var i in Images){
var t=Images[i];
Images[i]=new Image();
Images[i].src=t;
Images[i].onload = function (){
imC++;
if(imC == imN){
console.log("Load Completed");
preloaded = 1;
}
}
}
}
and
var Images = {
one image: "path/to/1.png",
....
}
then
if( preloaded == 1 ){
start_your_page();
}

Here the code that will remove the img tag and replace it with a new one:
document.getElementsByTagName('img')[0].addEventListener('mouseover', function() {
var parent = document.getElementsByTagName('img')[0].parentElement;
parent.removeChild(document.getElementsByTagName('img')[0]);
var new_img = document.createElement("img");
new_img.src = "https://upload.wikimedia.org/wikipedia/commons/6/69/600x400_kastra.jpg";
parent.appendChild(new_img);
});
<img src="https://www.w3schools.com/w3images/fjords.jpg">

I resolved the issue using code:
function displayImage() {
let image = new image();
image.src="source/of/image/returned/from/service";
image.addEventListener('load', function () {
document.getElementsByTagName('img')[0].src = image.src;
},false);
}
Here in code, I am attaching load event to image, source of image will be changed after image is loaded.

Issue with image load recursive chain on slow network/mobile

So basically I have a page with a few sections. Each sections contains 5-30 image icons that are fairly small in size but large enough that I want to manipulate the load order of them.
I'm using a library called collagePlus which allows me to give it a list of elements which it will collage into a nice image grid. The idea here is to start at the first section of images, load the images, display the grid, then move on to the next section of images all the way to the end. Once we reach the end I pass a callback which initializes a gallery library I am using called fancybox which simply makes all the images interactive when clicked(but does not modify the icons state/styles).
var fancyCollage = new function() { /* A mixed usage of fancybox.js and collagePlus.js */
var collageOpts = {
'targetHeight': 200,
'fadeSpeed': 2000,
'allowPartialLastRow': true
};
// This is just for the case that the browser window is resized
var resizeTimer = null;
$(window).bind('resize', function() {
resetCollage(); // resize all collages
});
// Here we apply the actual CollagePlus plugin
var collage = function(elems) {
if (!elems)
elems = $('.Collage');
elems.removeWhitespace().collagePlus(collageOpts);
};
var resetCollage = function(elems) {
// hide all the images until we resize them
$('.Collage .Image_Wrapper').css("opacity", 0);
// set a timer to re-apply the plugin
if (resizeTimer) clearTimeout(resizeTimer);
resizeTimer = setTimeout(function() {
collage(elems);
}, 200);
};
var setFancyBox = function() {
$(".covers").fancybox({/*options*/});
};
this.init = function(opts) {
if (opts != null) {
if (opts.height) {
collageOpts.targetHeight = opts.height;
}
}
$(document).ready(function() {
// some recursive functional funk
// basically goes through each section then each image in each section and loads the image and recurses onto the next image or section
function loadImage(images, imgIndex, sections, sectIndex, callback) {
if (sectIndex == sections.length) {
return callback();
}
if (imgIndex == images.length) {
var c = sections.eq(sectIndex);
collage(c);
images = sections.eq(sectIndex + 1).find("img.preload");
return loadImage(images, 0, sections, sectIndex + 1, callback);
}
var src = images.eq(imgIndex).data("src");
var img = new Image();
img.onload = img.onerror = function() {
images[imgIndex].src = src; // once the image is loaded set the UI element's source
loadImage(images, imgIndex + 1, sections, sectIndex, callback)
};
img.src = src; // load the image in the background
}
var firstImgList = $(".Collage").eq(0).find("img.preload");
loadImage(firstImgList, 0, $(".Collage"), 0, setFancyBox);
});
}
}
From my galleries I then call the init function.
It seems like my recursive chain being triggered by img.onload or img.onerror is not working properly if the images take a while to load(on slow networks or mobile). I'm not sure what I'm missing here so if anyone can chip in that would be great!
If it isn't clear what is going wrong from the code I posted you can see a live example here: https://www.yuvalboss.com/albums/olympic-traverse-august-2017
It works quite well on my desktop, but on my Nexus 5x it does not work and seems like the finally few collage calls are not happening. I've spent too long on this now so opening this up to see if I can get some help. Thanks everyone!

Whooooo I figured it out!
Was getting this issue which I'm still unsure about what it means
[Violation] Forced reflow while executing JavaScript took 43ms
Moved this into the callback that happens only once all images are loaded
$(window).bind('resize', function() {
resetCollage(); // resize all collages
});
For some reason it was getting called early even if the browser never resized causing collage to get called when no elements existed yet.
If anyone has any informative input as to why I was getting this js violation would be great to know so I can make a better fix but for now this works :):):)

jQuery or Javascript check if image loaded

I know there is a lot of these on Stackoverflow but I haven't found one that works for me in a recent version of jquery (1.10.2).
I did try:
$(".lazy").load(function (){}
But I believe after some research using .load to detect image load is deprecated in jQuery 1.8. What I need to do is fire an image resize function once the images are loaded. I don't have control over the
HTML and at the moment I am having to add the image dimensions via jQuery by attaching an attribute (via .attr()) once page loads so that I can use lazyload js.
The problem is that I need an accurate way to hold off all my various scripts until the image has loaded properly else the functions sometimes fire before every image had loaded. I have tried using $(window).load(function (){}); however it sometimes still fires before every image had loaded.

I usually do this:
var image = new Image();
image.onload = function () {
console.info("Image loaded !");
//do something...
}
image.onerror = function () {
console.error("Cannot load image");
//do something else...
}
image.src = "/images/blah/foo.jpg";
Remember that the loading is asynchronous so you have to continue the script inside the onload and onerror events.

There's also a useful .complete property of an image object, you can use it if you have already set the .src of your <img> before attaching to it any event listeners:
var img=document.getElementById('myimg');
var func=function(){
// do your code here
// `this` refers to the img object
};
if(img.complete){
func.call(img);
}
else{
img.onload=func;
}
Reference: http://www.w3schools.com/jsref/prop_img_complete.asp

I would give the images that require this constraint a class like mustLoad where:
<img class="mustLoad" src="..." alt="" />
and then create a generic image load handler function, such as:
$('img.mustLoad').on('load',function(){
/* Fire your image resize code here */
});
Edit:
In response to your comments about deprecating .load() above, .load() was deprecated, in favor of .on('load') to reduce ambiguity between the onLoad event and Ajax loading.

In the case of waiting of loading multiple images:
var images = $("#div-with-images img");
var unloaded = images.length;
images.on('load', function(){
-- unloaded;
if (!unloaded) {
// here all images loaded, do your stuff
}
});

What I need to do is fire an image resize function once the images are loaded.
Are you sure that you need the image to be loaded? Waiting for an image to load before resizing it can cause a large jump in the page layout, especially if the images have large file sizes, such as animated GIFs.
Usually, for an image resize, you only need to know the intrinsic dimensions of the image. While there is no event to tell you this, it's easy enough to poll the images for the data. Something like this could be particularly effective:
<img src="..." data-resizeme="123" />
(function() {
var images, l, i, tmp;
if( document.querySelectorAll) {
images = [].slice.call(document.querySelectorAll("img[data-resizeme]"),0);
}
else {
tmp = document.getElementsByTagName("img");
images = [];
// browser compatibility is fun!
for( i=tmp.length-1; i>=0; i--) {
if( tmp[i].getAttribute("data-resizeme")) images.unshift(tmp[i]);
}
}
for( i=images.length-1; i>=0; i--) {
images[i].onload = resizeImage;
images[i].onerror = cancelImageResize;
}
var timer = setInterval(function() {
for( i=images.length-1; i>=0; i--) {
if( images[i].width) {
resizeImage.call(images[i]);
images[i].onload = null;
cancelImageResize.call(images[i]);
}
}
if( images.length == 0) clearInterval(timer);
},100); // adjust granularity as needed - lower number is more responsive.
function cancelImageResize() {
var i;
for( i=images.length-1; i>=0; i--) {
if( images[i] == this) {
images.splice(i,1);
break;
}
}
}
function resizeImage() {
console.log("Image "+this.src+" is "+this.width+"x"+this.height);
}
})();
Hope this helps!

How to do a process after completion of another one in JavaScript

I want to add an image by Javascript, then calculating the html element width as
window.onload=function(){
document.getElementById('x').addEventListener('click', function(e){
var el = document.getElementById('xx');
el.innerHTML = '<img src="img.jpg" />';
var width = el.offsetWidth;
.....
}, false);
}
but since JavaScript conduct all processes simultaneously, I will get the width of the element before loading the image. How can I make sure that the image has been loaded into the content; then calculating the element width?
UPDATE: Thanks for the answers, but I think there is a misunderstanding. img src="img.jpg" /> does not exist in the DOM document. It will be added later by Javascript. Then, when trying to catch the element by Id, it is not there probably.

You can give the img an ID and do the following :-
var heavyImage = document.getElementById("my-img");//assuming your img ID is my-img
heavyImage.onload = function(){
//your code after image is fully loaded
}

window.onload=function(){
document.getElementById('x').addEventListener('click', function(e){
var el = document.getElementById('xx');
var img = new Image();//dynamically create image
img.src = "img.jpg";//set the src
img.alt = "alt";
el.appendChild(img);//append the image to the el
img.onload = function(){
var width = el.offsetWidth;
}
}, false);
}

This is untested, but if you add the image to the DOM, set an onload/load event-handler and then assign the src of the image, the event-handling should fire (once it's loaded) and allow you to find the width.
This is imperfect, though, since if the image is loaded from the browser's cache the onload/load event may not fire at all (particularly in Chromium/Chrome, I believe, though this is from memory of a bug that may, or may not, have since been fixed).

For the chrome bug you can use the following:-
var BLANK = 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==';//create a blank source
var tImg = document.getElementById("my-img");//get the image
var origSrc = tImg.src;//get the original src
tImg.src = BLANK;//change the img src to blank.
tImg.src = origSrc;//Change it back to original src. This will lead the chrome to load the image again.
tImg.onload= function(){
//your code after the image load
}

You can use a library called PreloadJS or you can try something like this:
//Somewhere in your document loading:
loadImage(yourImage, callbackOnComplete);
function loadImage(image, callbackOnComplete){
var self = this;
if(!image.complete)
window.content.setTimeout(
function() { self.loadImage(image, callbackOnComplete)}
,1000);
else callbackOnComplete();
}
I did this when I worked with images base64 which delay on loading.

Variable values aren't available for use after image.onload?

I'm using Canvas to perform a couple of things on an image which is loaded/drawn using image.onload & context.drawImage combo. I'm calculating the bounding size for scaling the images using a simple function which returns the values. I need those values for use at a later point in my code, but no matter what I do, I'm not able to assign the values to a variable. I'm also not able to access my Canvas's styleheight/stylewidth attributes after I assign it the calculated dimensions.
Here's a pseudos ample of my code
$(document).ready(function(){
//Canvas access, context reference etc here.
//Since I'm assigning styles to the canvas on the fly, the canvas has no ht/wdt yet
var dimes = '';
var image = new Image();
image.onload = function(){
//Apply original image height/width as canvas height/width 'attributes'
//(so that I can save the original sized image)
//Check if the image is larger than the parent container
//Calculate bounds if not
//Apply calculated dimensions as 'style' height/width to the canvas, so that the image fits
dimes = scaleImage(...);
//Works!
console.log(dimes);
//Rest all code
}
image.src = '...';
//Blank!!!
console.log(dimes);
//These all blank as well!!!
jQuery('#mycanvas').height() / width() / css('height') / css('width');
document.getElementById(canvas).style.height / .style.width / height / width;
});
I need to access the calculated dimensions for a 'reset' kind of function, that resets my canvas with the drawn image to the calculated size.

As #apsillers noted, the console.log(dimes) code is being executed after you simply define the image.onload() event handler.
If you want to access dimes outside of image.onload(), you'll need to ensure it's being executed after the image loads... e.g. as a response to a button click.
Put the var dimes = ""; before the $(document).ready() to make it a global variable.
Then if you need to access dimes in an event handler, it's ready for you:
$(document).ready(function() {
var image = new Image();
var dimes = "";
image.onload = function() {
dimes = scaleImage(...);
};
$(button).click(function() {
if (dimes === "") {
// image is not yet loaded
} else {
console.log(dimes);
}
});
});
Of course, dimes will now only be accessible inside this first $(document).ready() event handler. If you add another one (which you can certainly do in jQuery), you'll need to use the $.fn.data() jQuery object method to store dimes:
$(document).ready(function() {
var image;
$(document).data("dimes", ""); // initializes it
image.onload = function() {
$(document).data("dimes", scaleImage(...));
};
});
// some other code
$(document).ready(function() {
$("#myButton").click(function() {
var dimes = $(document).data("dimes");
if (dimes === "") {
// image not yet loaded
} else {
console.log(dimes);
}
});
});

Your img.onload function can run only after the JavaScript execution thread stops being busy, i.e., after your ready function completes. Thus, your console.log(dimes) call is running before your onload function.
Put any code that needs to use dimes inside of the onload function. Otherwise, the code the needs to use dimes might run before the onload handler fires.

http://jsfiddle.net/KxTny/1/
$(document).ready(function(){
var dimes = 0;
var width = 20;
var height = 30;
pass(dimes, width, height);
});​
function pass(dimes, width, height) {
alert(dimes);
alert(height);
alert(width);
}