Develop Reference

problem on onclick() event for more than one clicks done on a div

i have an html page where,when hovered over the first image a second image fades in/is shown.The first image has an onclick() event which performs a transition of rotating the image and scaling it by some number.During the transition, the first image disappears and some text appears on the same place(area of the div tag of the first image).I perform the transition through javascript and the hovering animation using css. Now when i click on the text(or the area of the div tag) the transition must reverse back i.e., the div area must be as it was before clicking(even with the hovering working.). I would like to know the answer through pure javascript please.
Thank you in advance.
timesclicked = 0;
document.getElementById("hoverImage").addEventListener("click", function()
{
var x = document.getElementById('container');
timesclicked+=1;
if(timesclicked%2!=0)
{
//obj.style.opacity = '0.5';
x.style.transform = 'rotateZ(-360deg) scale(1.4)';
x.style.transition = 'all 1.5s ease-in-out';
setTimeout(() => {
x.innerHTML = '<div style="font-size:16px; font-family: monospace; font-weight:bold; text-align:center; "> My Hero Academia, abbreviated as HeroAca is a Japanese superhero manga series written and illustrated by Kōhei Horikoshi. It has been serialized in Weekly Shōnen Jump since July 2014, and, as of February 2019, 22 volumes have been collected in tankōbon format.</div>'},'1300');
}
else
{
x.style.transform = 'rotateZ(-45deg) scale(1)';
x.style.transition = 'all 1.5s ease-in-out';
setTimeout(() => {
x.innerHTML = '<img src="https://picsum.photos/300">'},'500');
}
});
img
{
width: 300px;
height: 300px;
}
#mainImage,#hoverImage
{
left: 0px;
position: absolute;
top: 0px;
}
#hoverImage
{
opacity: 0;
transition: opacity 0.4s 0.1s ;
}
#hoverImage:hover
{
opacity: 1;
}
#container
{
background: url(https://picsum.photos/300);
background-size: cover;
width: 300px;
height: 300px;
position: absolute;
top:20%;
left:40%;
transform: rotateZ(-45deg);
}
#container:before
{
content: "";
display: block;
position: fixed;
width: 100%;
height: 100%;
left: 0;
top: 0;
z-index: -1;
background-color: rgba(255, 255, 255, 0.6);
}
<div id="container" >
<img id="mainImage" src="https://picsum.photos/300">
<img id="hoverImage" src="https://picsum.photos/300">
</div>
As much as i know, I think the second clicking event is not happening because the eventlistener is on the hoverImage. I need a way to run the else part of the code somehow.

It looks like there are a few problems with your code, and you're going to have some debugging to do. That said, try this for a strategy:
Put your on-click event on the #container.
Put all the styling and transitioning details in the css. Your javascript will just add and remove a class from the #container.
Don't track the number of clicks unless you need it for something else. Have your if statement check for the presence or absence of the class you're toggling. (Or use an explicit toggle instead of an if-else block.)
Don't add and remove the text and background in the javascript, put them both in the HTML and control their visibility using the CSS.
edit:
People asked for examples and clarification. I'm stealing some of this from other people's answers.
I'm not completely sure I've understood OP's intentions correctly, and there are some rough-around-the-edgues details (like the cursor when you hover before clicking), but I think this should serve as an example:
let container = document.getElementById("container");
container.addEventListener("click", function(){
container.classList.toggle("selected");
});
#mainImage, #hoverImage, #selectedText {
width: 300px;
height: 300px;
left: 0px;
position: absolute;
top: 0px;
}
#hoverImage {
opacity: 0;
transition: opacity 0.4s 0.1s;
}
#container:hover > #hoverImage {
opacity: 1;
}
#container {
width: 300px;
height: 300px;
position: absolute;
top:20%;
left:40%;
transform: rotateZ(-45deg);
transition: all 1.5s ease-in-out;
}
#container.selected {
transform: rotateZ(-360deg) scale(1.4);
}
#container:before {
content: "";
display: block;
position: fixed;
width: 100%;
height: 100%;
left: 0;
top: 0;
z-index: -1;
background-color: rgba(255, 255, 255, 0.6);
}
#selectedText {
font-size:16px;
font-family: monospace;
font-weight:bold;
text-align:center;
background: url(https://picsum.photos/300?text);
background-size: cover;
opacity: 0;
transition: opacity 0.1s 0.5s;
}
#container.selected > #selectedText {
opacity: 1;
transition: opacity 0.1s 1.3s;
}
<div id="container">
<img id="mainImage" src="https://picsum.photos/300?main">
<img id="hoverImage" src="https://picsum.photos/300?hover">
<div id="selectedText">
My Hero Academia, abbreviated as HeroAca is a Japanese superhero
manga series written and illustrated by Kōhei Horikoshi. It has been
serialized in Weekly Shōnen Jump since July 2014, and, as of
February 2019, 22 volumes have been collected in tankōbon format.
</div>
</div>

you can add the click event listener on the container div.
timesclicked = 0;
document.getElementById("container").addEventListener("click", function()
{
var x = document.getElementById('container');
timesclicked+=1;
if(timesclicked%2!=0)
{
//obj.style.opacity = '0.5';
x.style.transform = 'rotateZ(-360deg) scale(1.4)';
x.style.transition = 'all 1.5s ease-in-out';
setTimeout(() => {
x.innerHTML = '<div style="font-size:16px; font-family: monospace; font-weight:bold; text-align:center; "> My Hero Academia, abbreviated as HeroAca is a Japanese superhero manga series written and illustrated by Kōhei Horikoshi. It has been serialized in Weekly Shōnen Jump since July 2014, and, as of February 2019, 22 volumes have been collected in tankōbon format.</div>'},'1300');
}
else
{
x.style.transform = 'rotateZ(-45deg) scale(1)';
x.style.transition = 'all 1.5s ease-in-out';
setTimeout(() => {
x.innerHTML = '<img src="https://picsum.photos/300">'},'500');
}
});
img
{
width: 300px;
height: 300px;
}
#mainImage,#hoverImage
{
left: 0px;
position: absolute;
top: 0px;
}
#hoverImage
{
opacity: 0;
transition: opacity 0.4s 0.1s ;
}
#hoverImage:hover
{
opacity: 1;
}
#container
{
background: url(https://picsum.photos/300);
background-size: cover;
width: 300px;
height: 300px;
position: absolute;
top:20%;
left:40%;
transform: rotateZ(-45deg);
}
#container:before
{
content: "";
display: block;
position: fixed;
width: 100%;
height: 100%;
left: 0;
top: 0;
z-index: -1;
background-color: rgba(255, 255, 255, 0.6);
}
<div id="container" >
<img id="mainImage" src="https://picsum.photos/300">
<img id="hoverImage" src="https://picsum.photos/300">
</div>
</style>

if I understand your problem correctly, I think you just need to move the transition styles into your CSS
x.style.transition = 'all 1.5s ease-in-out';

onClick add/remove class inside loop is not working in jquery

I'm working on flexslider here onClick next I want to add class it is working but randomly click is coming when I first click class added then on second click not coming third click coming so on. I want to add a class every click. Here might be the problem in if()
$('.flex-next').on('click', function() {
if ($('.timeline span').hasClass('clicked')) {
$('.timeline span.clicked').removeClass('clicked');
$(this).addClass('clicked');
} else {
$('.timeline span').removeClass('clicked');
$('.timeline span').addClass('clicked');
}
});
.timeline {
content: '';
background-color: rgba(255, 255, 255, 0.52);
display: block;
width: 100px;
height: 2px;
-webkit-transform: rotate(-90deg);
transform: rotate(-90deg);
position: relative;
}
.timeline span:before {
position: absolute;
left: 0;
top: -1px;
content: '';
background-color: red;
display: block;
height: 3px;
animation: yourAnimation 1s 0s linear;
}
.timeline span.clicked {
position: absolute;
left: 0;
top: -1px;
content: '';
background-color: blue;
display: block;
height: 3px;
animation: yourAnimation 1s 0s linear;
}
#keyframes yourAnimation {
0% {
width: 0;
}
50% {
width: 50%;
}
82% {
width: 100%;
}
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="flex-next">Click here</div>
<span class="timeline">
<span></span>
</span>

You can acheive the required functionality as
$('.flex-next').on('click', function(){
if (! ($('.timeline span').hasClass('clicked')) ) {
$('.timeline span').addClass('clicked');
setTimeOut(function(){
$('.timeline span').removeClass('clicked');
} , 200)
}
});

To add/remove a class on click, it is better to use jquery toggleClass function.
Moreover you may need to execute the click event after the document is loaded correctly
$( document ).ready(function() {
$('.flex-next').on('click', function(){
$('.timeline span').toggleClass( "clicked" );
});
});
For more info, you may refer to: http://api.jquery.com/toggleclass/

How to change background color every n-seconds?

So a while back I think i saw an effect on some site that was transitioning between different background colors (changing background colors).
The color changed like every 2-3 seconds.
The transitions were pretty smooth as well. I found it pretty cool.
I'm redesigning my services website and would like to add that effect to my site.
There are 2 variables that need to be controlled: time and color.
P.S. Not trying to get anyone to write the code for me, but could you please refer me to some links where I can find out about this effect.
Would be great if you could tell me the name of this effect and the library it exists in.

Here's JS Fiddle that shows you some #keyframes in combo with the js to slow down timing via click. Hope that helps!
.body {
width: 100%;
height: 1000px;
animation-name: colorChange;
animation-duration: 10s;
animation-iteration-count: infinite;
text-align: center;
}
#keyframes colorChange {
0% {
background: red;
}
20% {
background: blue;
}
40% {
background: green;
}
60% {
background: orange;
}
80% {
background: purple;
}
100% {
background: red;
}
}
.button {
padding: 10px;
margin-top: 40px;
font-size: 20px;
}
$( ".button" ).on( "click", function () {
$( ".body" ).css( "animation-duration", "20s" )
})
Edit
Added snippet.
$( ".button" ).on( "click", function () {
$( ".body" ).css( "animation-duration", "20s" )
})
.body {
width: 100%;
height: 1000px;
animation-name: colorChange;
animation-duration: 10s;
animation-iteration-count: infinite;
text-align: center;
}
#keyframes colorChange {
0% {
background: red;
}
20% {
background: blue;
}
40% {
background: green;
}
60% {
background: orange;
}
80% {
background: purple;
}
100% {
background: red;
}
}
.button {
padding: 10px;
margin-top: 40px;
font-size: 20px;
}
<div class="body">
<button class="button">Change Timing</button>
</div>

To change your website background color in a defined time interval you can follow the bellow link.
http://www.cakephpexample.com/html/add-gradient-effect-to-your-website-by-javascript/
Where a complete example given with source code.

You can possibly do it with CSS3 animation keyframes.
Take a look at this Fun With Pulsing Background Colors in CSS3.

CSS3 page loading effect trigger by jquery

Hi friends I am trying to make CSS3 animation which will be trigger by jquery. Ie when the user submit some form I need to display animation (css3) for some duration and redirect it to the next page.
CSS3 animation:
.circle {
background-color: rgba(0,0,0,0);
border: 5px solid rgba(0,183,229,0.9);
opacity: .9;
border-right: 5px solid rgba(0,0,0,0);
border-left: 5px solid rgba(0,0,0,0);
border-radius: 50px;
box-shadow: 0 0 35px #2187e7;
width: 50px;
height: 50px;
margin: 0 auto;
-moz-animation: spinPulse 1s infinite ease-in-out;
-webkit-animation: spinPulse 1s infinite linear;
}
.circle1 {
background-color: rgba(0,0,0,0);
border: 5px solid rgba(0,183,229,0.9);
opacity: .9;
border-left: 5px solid rgba(0,0,0,0);
border-right: 5px solid rgba(0,0,0,0);
border-radius: 50px;
box-shadow: 0 0 15px #2187e7;
width: 30px;
height: 30px;
margin: 0 auto;
position: relative;
top: -50px;
-moz-animation: spinoffPulse 1s infinite linear;
-webkit-animation: spinoffPulse 1s infinite linear;
}
#-moz-keyframes spinPulse {
0% {
-moz-transform: rotate(160deg);
opacity: 0;
box-shadow: 0 0 1px #2187e7;
}
50% {
-moz-transform: rotate(145deg);
opacity: 1;
}
100% {
-moz-transform: rotate(-320deg);
opacity: 0;
};
}
#-moz-keyframes spinoffPulse {
0% {
-moz-transform: rotate(0deg);
}
100% {
-moz-transform: rotate(360deg);
};
}
#-webkit-keyframes spinPulse {
0% {
-webkit-transform: rotate(160deg);
opacity: 0;
box-shadow: 0 0 1px #2187e7;
}
50% {
-webkit-transform: rotate(145deg);
opacity: 1;
}
100% {
-webkit-transform: rotate(-320deg);
opacity: 0;
};
}
#-webkit-keyframes spinoffPulse {
0% {
-webkit-transform: rotate(0deg);
}
100% {
-webkit-transform: rotate(360deg);
};
}
This is html
<div class="circle"></div>
<div class="circle1"></div>
<button class="next" name="submit" id = "submit"></button>
Now when I user click on I need to display this effect for a fraction of time (some thing like alert box I mean while this animation is playing user shouldnt be able to do anything in the rest of the page)

Usually you make the page inaccessible by covering it with an element - an "overlay".
HTML:
<div class="loadingOverlay">
<div class="circle"></div> <!-- it makes sense to put these inside -->
<div class="circle1"></div>
</div>
CSS:
.loadingOverlay {
position: fixed;
top: 0;
bottom: 0;
left: 0;
right: 0;
}
To activate it when the user clicks the submit button, just make it "hidden" by default. And when the user clicks the button, make it "visible". In it's most basic form:
$('#submit').on('click', function () {
$loadingOverlay.css('display', 'block');
});
and the extra needed CSS:
.loadingOverlay {
/* ... */
display: none;
}
On the example I provide below you won't see the animation. The next page, by being blank, just loads too quickly. But you will see it on a "real" website situation.
Here's the live example: http://jsfiddle.net/9H7wf/2/
EDIT:
Max Boll suggested having the "loading effect" happening on the "new" page. It makes sense. But while a new page is being fetched, the "old" one still remains visible until a few key "http" things happen. See http://www.stevesouders.com/blog/2012/12/03/the-perception-of-speed/
So, it does make sense to have it on the "old" page.

I'd suggest you to use jQuery for this.
By default you could display your animation as an overlay (as JOPLOmacedo said).
Then you add the following to your javascript:
$(document).ready(function() {
$('.loadingOverlay').fadeOut();
});
This will show the loading overlay as long as the site needs to load (which you actually wanna show by that loading animation). Once the page is loaded, this javascript will fade it out.
My solution is based on JOPLOmacedo's answer.
EDIT
I just saw your new comment. To show it on button click, you can do it like this:
$(document).ready(function() {
$('.button').click(function() {
$('.loadingOverlay').fadeIn();
});
});
Inside of the click event function you could start an interval to fade it out again after X seconds.

Hi Friends I found a solution to this one Thanx #JOPLOmacedo for helping me to fix this one
$function(){
$('#submit').click(function(){
$('.loadingOverlay').css('display', 'block');
function complete() {
$('.loadingOverlay').css('display', 'none');
}
$('.circle').hide().fadeIn(1000,complete);
$('.cirlce1').hide().fadeIn(1000,complete);
});
}

How to show Page Loading div until the page has finished loading?

I have a section on our website that loads quite slowly as it's doing some intensive calls.
Any idea how I can get a div to say something similar to "loading" to show while the page prepares itself and then vanish when everything is ready?

Original Answer
I've needed this and after some research I came up with this (jQuery needed):
First, right after the <body> tag add this:
<div id="loading">
<img id="loading-image" src="path/to/ajax-loader.gif" alt="Loading..." />
</div>
Then add the style class for the div and image to your CSS:
#loading {
position: fixed;
display: block;
width: 100%;
height: 100%;
top: 0;
left: 0;
text-align: center;
opacity: 0.7;
background-color: #fff;
z-index: 99;
}
#loading-image {
position: absolute;
top: 100px;
left: 240px;
z-index: 100;
}
Then, add this javascript to your page (preferably at the end of your page, before your closing </body> tag, of course):
<script>
$(window).load(function() {
$('#loading').hide();
});
</script>
Finally, adjust the position of the loading image and the background-color of the loading div with the style class.
This is it, should work just fine. But of course you should have an ajax-loader.gif somewhere or use base64 url for image's src value. Freebies here. (Right-click > Save Image As...)
Update
For jQuery 3.0 and above you can use:
<script>
$(window).on('load', function () {
$('#loading').hide();
})
</script>
Update
The original answer is from jQuery and before flexbox era. You can use many view management libraries / frameworks now like Angular, React and Vue.js. And for CSS you have flexbox option. Below is CSS alternative:
#loading {
position: fixed;
display: flex;
justify-content: center;
align-items: center;
width: 100%;
height: 100%;
top: 0;
left: 0;
opacity: 0.7;
background-color: #fff;
z-index: 99;
}
#loading-image {
z-index: 100;
}

This script will add a div that covers the entire window as the page loads. It will show a CSS-only loading spinner automatically. It will wait until the window (not the document) finishes loading, then it will wait an optional extra few seconds.
Works with jQuery 3 (it has a new window load event)
No image needed but it's easy to add one
Change the delay for more branding or instructions
Only dependency is jQuery.
CSS loader code from https://projects.lukehaas.me/css-loaders
$('body').append('<div style="" id="loadingDiv"><div class="loader">Loading...</div></div>');
$(window).on('load', function(){
setTimeout(removeLoader, 2000); //wait for page load PLUS two seconds.
});
function removeLoader(){
$( "#loadingDiv" ).fadeOut(500, function() {
// fadeOut complete. Remove the loading div
$( "#loadingDiv" ).remove(); //makes page more lightweight
});
}
.loader,
.loader:after {
border-radius: 50%;
width: 10em;
height: 10em;
}
.loader {
margin: 60px auto;
font-size: 10px;
position: relative;
text-indent: -9999em;
border-top: 1.1em solid rgba(255, 255, 255, 0.2);
border-right: 1.1em solid rgba(255, 255, 255, 0.2);
border-bottom: 1.1em solid rgba(255, 255, 255, 0.2);
border-left: 1.1em solid #ffffff;
-webkit-transform: translateZ(0);
-ms-transform: translateZ(0);
transform: translateZ(0);
-webkit-animation: load8 1.1s infinite linear;
animation: load8 1.1s infinite linear;
}
#-webkit-keyframes load8 {
0% {
-webkit-transform: rotate(0deg);
transform: rotate(0deg);
}
100% {
-webkit-transform: rotate(360deg);
transform: rotate(360deg);
}
}
#keyframes load8 {
0% {
-webkit-transform: rotate(0deg);
transform: rotate(0deg);
}
100% {
-webkit-transform: rotate(360deg);
transform: rotate(360deg);
}
}
#loadingDiv {
position:absolute;;
top:0;
left:0;
width:100%;
height:100%;
background-color:#000;
}
This script will add a div that covers the entire window as the page loads. It will show a CSS-only loading spinner automatically. It will wait until the window (not the document) finishes loading.
<ul>
<li>Works with jQuery 3, which has a new window load event</li>
<li>No image needed but it's easy to add one</li>
<li>Change the delay for branding or instructions</li>
<li>Only dependency is jQuery.</li>
</ul>
Place the script below at the bottom of the body.
CSS loader code from https://projects.lukehaas.me/css-loaders
<!-- Place the script below at the bottom of the body -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

window.onload = function(){ document.getElementById("loading").style.display = "none" }
#loading {width: 100%;height: 100%;top: 0px;left: 0px;position: fixed;display: block; z-index: 99}
#loading-image {position: absolute;top: 40%;left: 45%;z-index: 100}
<div id="loading">
<img id="loading-image" src="img/loading.gif" alt="Loading..." />
</div>
Page loading image with simplest fadeout effect created in JS:

I have another below simple solution for this which perfectly worked for me.
First of all, create a CSS with name Lockon class which is transparent overlay along with loading GIF as shown below
.LockOn {
display: block;
visibility: visible;
position: absolute;
z-index: 999;
top: 0px;
left: 0px;
width: 105%;
height: 105%;
background-color:white;
vertical-align:bottom;
padding-top: 20%;
filter: alpha(opacity=75);
opacity: 0.75;
font-size:large;
color:blue;
font-style:italic;
font-weight:400;
background-image: url("../Common/loadingGIF.gif");
background-repeat: no-repeat;
background-attachment: fixed;
background-position: center;
}
Now we need to create our div with this class which cover entire page as an overlay whenever the page is getting loaded
<div id="coverScreen" class="LockOn">
</div>
Now we need to hide this cover screen whenever the page is ready and so that we can restrict the user from clicking/firing any event until the page is ready
$(window).on('load', function () {
$("#coverScreen").hide();
});
Above solution will be fine whenever the page is loading.
Now the question is after the page is loaded, whenever we click a button or an event which will take a long time, we need to show this in the client click event as shown below
$("#ucNoteGrid_grdViewNotes_ctl01_btnPrint").click(function () {
$("#coverScreen").show();
});
That means when we click this print button (which will take a long time to give the report) it will show our cover screen with GIF which gives result and once the page is ready above windows on load function will fire and which hide the cover screen once the screen is fully loaded.

Default the contents to display:none and then have an event handler that sets it to display:block or similar after it's fully loaded. Then have a div that's set to display:block with "Loading" in it, and set it to display:none in the same event handler as before.

Here's the jQuery I ended up using, which monitors all ajax start/stop, so you don't need to add it to each ajax call:
$(document).ajaxStart(function(){
$("#loading").removeClass('hide');
}).ajaxStop(function(){
$("#loading").addClass('hide');
});
CSS for the loading container & content (mostly from mehyaa's answer), as well as a hide class:
#loading {
width: 100%;
height: 100%;
top: 0px;
left: 0px;
position: fixed;
display: block;
opacity: 0.7;
background-color: #fff;
z-index: 99;
text-align: center;
}
#loading-content {
position: absolute;
top: 50%;
left: 50%;
text-align: center;
z-index: 100;
}
.hide{
display: none;
}
HTML:
<div id="loading" class="hide">
<div id="loading-content">
Loading...
</div>
</div>

Well, this largely depends on how you're loading the elements needed in the 'intensive call', my initial thought is that you're doing those loads via ajax. If that's the case, then you could use the 'beforeSend' option and make an ajax call like this:
$.ajax({
type: 'GET',
url: "some.php",
data: "name=John&location=Boston",
beforeSend: function(xhr){ <---- use this option here
$('.select_element_you_want_to_load_into').html('Loading...');
},
success: function(msg){
$('.select_element_you_want_to_load_into').html(msg);
}
});
EDIT
I see, in that case, using one of the 'display:block'/'display:none' options above in conjunction with $(document).ready(...) from jQuery is probably the way to go. The $(document).ready() function waits for the entire document structure to be loaded before executing (but it doesn't wait for all media to load). You'd do something like this:
$(document).ready( function() {
$('table#with_slow_data').show();
$('div#loading image or text').hide();
});

My blog will work 100 percent.
function showLoader()
{
$(".loader").fadeIn("slow");
}
function hideLoader()
{
$(".loader").fadeOut("slow");
}
.loader {
position: fixed;
left: 0px;
top: 0px;
width: 100%;
height: 100%;
z-index: 9999;
background: url('pageLoader2.gif') 50% 50% no-repeat rgb(249,249,249);
opacity: .8;
}
<div class="loader"></div>

Create a <div> element that contains your loading message, give the <div> an ID, and then when your content has finished loading, hide the <div>:
$("#myElement").css("display", "none");
...or in plain JavaScript:
document.getElementById("myElement").style.display = "none";

This will be in synchronisation with an api call, When the api call is triggered, the loader is shown. When the api call is succesful, the loader is removed. This can be used for either page load or during an api call.
$.ajax({
type: 'GET',
url: url,
async: true,
dataType: 'json',
beforeSend: function (xhr) {
$( "<div class='loader' id='searching-loader'></div>").appendTo("#table-playlist-section");
$("html, body").animate( { scrollTop: $(document).height() }, 100);
},
success: function (jsonOptions) {
$('#searching-loader').remove();
.
.
}
});
CSS
.loader {
border: 2px solid #f3f3f3;
border-radius: 50%;
border-top: 2px solid #3498db;
width: 30px;
height: 30px;
margin: auto;
-webkit-animation: spin 2s linear infinite; /* Safari */
animation: spin 2s linear infinite;
margin-top: 35px;
margin-bottom: -35px;
}
/* Safari */
#-webkit-keyframes spin {
0% { -webkit-transform: rotate(0deg); }
100% { -webkit-transform: rotate(360deg); }
}
#keyframes spin {
0% { transform: rotate(0deg); }
100% { transform: rotate(360deg); }
}

for drupal in your theme
custom_theme.theme file
function custom_theme_preprocess_html(&$variables) {
$variables['preloader'] = 1;
}
In html.html.twig file after skip main content link in body
{% if preloader %}
<div id="test-preloader" >
<div id="preloader-inner" class="cssload-container">
<div class="wait-text">{{ 'Please wait...'|t }} </div>
<div class="cssload-item cssload-moon"></div>
</div>
</div>
{% endif %}
in css file
#test-preloader {
position: fixed;
background: white;
width: 100%;
height: 100%;
top: 0;
left: 0;
z-index: 9999;
}
.cssload-container .wait-text {
text-align: center;
padding-bottom: 15px;
color: #000;
}
.cssload-container .cssload-item {
margin: auto;
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
width: 131px;
height: 131px;
background-color: #fff;
box-sizing: border-box;
-o-box-sizing: border-box;
-ms-box-sizing: border-box;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-shadow: 0 0 21px 3px rgba(130, 130, 130, 0.26);
-o-box-shadow: 0 0 21px 3px rgba(130, 130, 130, 0.26);
-ms-box-shadow: 0 0 21px 3px rgba(130, 130, 130, 0.26);
-webkit-box-shadow: 0 0 21px 3px rgba(130, 130, 130, 0.26);
-moz-box-shadow: 0 0 21px 3px rgba(130, 130, 130, 0.26);
}
.cssload-container .cssload-moon {
border-bottom: 26px solid #008AFA;
border-radius: 50%;
-o-border-radius: 50%;
-ms-border-radius: 50%;
-webkit-border-radius: 50%;
-moz-border-radius: 50%;
animation: spin 1.45s ease infinite;
-o-animation: spin 1.45s ease infinite;
-ms-animation: spin 1.45s ease infinite;
-webkit-animation: spin 1.45s ease infinite;
-moz-animation: spin 1.45s ease infinite;
}

I needed a splash screen, which I implemented by reusing parts of the solutions listed here. It uses Vanilla JS for full backwards-compatibility.
Step 1: Add a background with a spinner gif on top of the page, then remove them when everything is loaded.
body.has-js::before {
content: '';
position: fixed;
left: 0;
right: 0;
top: 0;
bottom: 0;
z-index: 10;
height: 100vh;
width: 100vw;
pointer-events: none;
transition: all .2s;
background: white url('/img/spinner.gif') no-repeat center center / 50px;
}
body.loaded::before {
opacity: 0;
width: 0;
height: 0;
}
Step 2: Add a little script right after the opening body tag to start displaying the load/splash screen.
<body>
<script>
// Only show loader if JS is available
document.body.className += ' has-js';
// Option 1: Hide loader when 'load' event fires
window.onload = function() { document.body.className += ' loaded'; }
// Option 2: Hide loader after 2 seconds, in case the 'load' event never fires
setTimeout(function(){ document.body.className += ' loaded'; }, 1000 * 2);
</script>
<!-- Page content goes after this -->
</body>

Based on #mehyaa answer, but much shorter:
HTML (right after <body>):
<img id = "loading" src = "loading.gif" alt = "Loading indicator">
CSS:
#loading {
position: absolute;
top: 50%;
left: 50%;
width: 32px;
height: 32px;
/* 1/2 of the height and width of the actual gif */
margin: -16px 0 0 -16px;
z-index: 100;
}
Javascript (jQuery, since I'm already using it):
$(window).load(function() {
$('#loading').remove();
});