Develop Reference

How to show loader overlay until image is loaded on webpage?

I want to make a loading overlay, but instead using setTimeout I would like to show the "loader" until the first image is fully loaded on the webpage. ( After that, I would like to use lazy image loading )
Until now I used setTimeout, but it's not working really well. I can set a bigger time, but now there is a "gap" between the loader and when the image appears.
The picture urls are fetched from a wordpress API and I'm using template.
What I want is to show the "loading" overlay until the first image is fully loaded, so users don't see the blank state.
var img = document.querySelector("#img");
img.onload = function(){
document.getElementById("loading").style.display = "none"
}
I can't use jQuery because it's for a school project. I tried all the alternatives I found here by adding a console.log("loaded") when it's loaded, but nothing seems to work.

Maybe set the img.src after you defined onload
let img = document.createElement('img');
img.onload = function(){}
img.src = "url"

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
});

How do I make .load() wait till everything is fully loaded? [duplicate]

I have a Python script that is doing some manipulation on a JPEG image. I pass some parameters to this script and call it from my HTML page. The script returns an img src="newimage.jpg tag.
I know how to wait for the reply from the script but I don't know how to tell when the image is fully loaded (when it is, I want to display it). What I get now is the image loading slowly so the user is seeing this "loading" process. Instead, I want to have a msg telling the user to wait while the image is loading, only then I want to display the image.

You can dynamically create a new image, bind something to its load event, and set the source:
$('<img>').bind('load', function() {
$(this).appendTo('body');
}).attr('src', image_source);

Image Loading
Wait for ajaxRequest

The other answers have mentioned how to do so with jQuery, but regardless of library that you use, ultimately you will be tying into the load event of the image.
Without a library, you could do something like this:
var el = document.getElementById('ImgLocation');
var img = document.createElement('img');
img.onload = function() {
this.style.display = 'block';
}
img.src = '/path/to/image.jpg';
img.style.display = 'none';
el.appendChild(img);

Replace img src but have loading graphic display while image is downloading

I have a page that swaps some fairly large images in and out. There are too many to preload when the page initially loads so that is not an option. So what I need to do is load them as they are requested by the user. Right now I'm using jQuery to replace the img's src. This works fine but the images I am loading can be around 500KB and it looks bad as they paint down the screen as they are downloading. What I'd like to do is pop a loading gif on the page when the image is in the process of loading then have the loading gif disappear once the image is loaded. I'm struggling to find a way to do that though. Here is the JS/jQuery code that I have that just replaces the src.
var product = "bowl";
var image = "dog.jpg"; //this is actually pulled from a data attribute, but its just hardcoded here for an example
$("#images img[data-product="+product+"]").attr("src", "/img/tablesetting/"+image);

I made a working jsfiddle showing this principle
http://jsfiddle.net/kasperfish/c72RT/4/
I recently needed to do the same thing. Basically I wrapped the image in a container div. within the container I've added a span element with my ajax loader gif embedded. this span has to be hidden initially but gets visible when an ajax request is made. The span gets removed when the image is fully loaded.
before ajax call
$('#your_image_container').find('span').show();
on success
$('#your_image').attr('src', 'your/image/url').load(function() {
$('#your_image_container').find('span').fadeOut();
});
I made a jsfiddle showing this principle
http://jsfiddle.net/kasperfish/c72RT/4/

Preload the image.
var product = "bowl";
var imageSrc = "dog.jpg";
var imgEl = $("#images img[data-product="+product+"]");
// show loading graphic only if it's needed
var timer = setTimeout(function(){
imgEl.attr("src", "/img/loading.gif");
},50);
// preload image
var img = new Image();
img.onload = function() {
clearTimeout(timer);
imgEl.attr("src",imageSrc);
}
img.src = imageSrc;

$img.attr("src", newImage);
if (!$img.get(0).complete) {
$img
.hide()
.after("<img src=throbber>")
.on("load", function () {
$(this).show().next().remove();
});
}

Image preloading ... the fastest way

I'm working on a project dealing with a high traffic webpage (really high!). On landing page tons of images are displayed (~40), that needs to be there, right after the page was loaded to display them by fading in. We don't use any library for this since it should be loaded before it was ready to use. We have 4 image servers. Does anybody have any experience which is the best way to load images? I tried the following:
In page header, right after the <head>, inserted a script tag:
<script>
var img = new Image(); img.src= "src of the image";
</script>
Doing so, images begin and finish to load before DOMReady and Load event. But images on the page with the same url seem to load again, even if they was loaded before. The urls are the same, caching was on, Mozilla was used.
Maybe there's some mechanism that prevents the browser to use those images? or what?
Another question: does it cause any slowdown, when DOM and images load parallel?

First, I would recommend using CSS sprites. You can find more information here:
http://www.alistapart.com/articles/sprites
Second, if you want to load the images on DOM ready, use the following:
function listen(event, elem, func) {
if (elem.addEventListener) {
elem.addEventListener(event, func, false);
} else if (elem.attachEvent) {
elem.attachEvent('on' + event, func);
}
}
listen('load', window, function() {
var img = new Image();
img.src= "src of the image";
});
Using sprites will cut your loading time in half. You eliminate the majority of your HTTP requests and the sprite sheets get cached right away so each subsequent page a user visits will already have it loaded.
EDIT
Here's a way to preload many images:
function preload(images) {
if (document.images) {
var imageArray = [];
imageArray = images.split(',');
var imageObj = new Image();
for (var i = 0; i < imageArray.length; i += 1) {
imageObj.src = imageArray[i];
}
}
}
Call the function like this:
preload('image1.jpg,image2.jpg,image3.jpg');