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javascript slideshow sometimes messes up

This one is driving me crazy. My javascript code works for most slides in a deck I create but sometimes it messes up. It usually takes one of four forms:
the slide will appear as a tiny picture under a logo I put on the slide when the slide isn't wide enough to fill the viewing area, or
the slide will appear properly sized but under the logo which now occupies the full height of the viewing area, or
both of the above, or
neither the slide nor the logo appear. Instead the previous slide continues to be shown.
My code isn't all that complicated. The part that shows the individual slide is below:
var backgroundImage;
var imgHeight;
var imgWidth;
function waitForHeight() {
sleep(120).then(() => {
if (imgHeight == 0) {
waitForHeight()
} else {
setBackground();
}
});
}
function getSizes() {
imgHeight = this.height;
imgWidth = this.width;
return true;
}
function showImage(imgPath) {
var myImage = new Image();
myImage.name = imgPath;
myImage.onload = getSizes;
myImage.src = imgPath;
return myImage;
}
function setBackground() {
var backgroundPosition = "";
var backgroundSize = "100%";
var aspectRatio = imgHeight / imgWidth;
if (aspectRatio > 0.70) {
backgroundSize = "10vw, auto 100%";
backgroundImage = "URL(images/LCI_emblem_2color.png), " + backgroundImage;
backgroundPosition = "top 1rem left 1rem, top right";
}
var mainPanel = document.getElementById("mainpanel")
mainPanel.style.backgroundImage = backgroundImage;
mainPanel.style.backgroundPosition = backgroundPosition;
mainPanel.style.backgroundSize = backgroundSize;
}
function addPic(curCell, curSlide, nodeNum) {
imgHeight = 0; // flag that height not set yet
var curImg = showImage(curSlide.childNodes[nodeNum].firstChild.nodeValue);
curImg.setAttribute('class', 'd-none d-md-block');
curCell.appendChild(curImg);
backgroundImage = "URL(" + getSlidePicture(curSlide) + ")";
waitForHeight();
}
The code, as I said, is not complicated. I can understand somewhat what the problem is - either the picture doesn't load or it gets put into the wrong "background" area, but I don't get why it happens.
I've noted the issue occurs with the same slides in both Chromium and Firefox and has survived multiple versions of each browser, so it's probably not a browser issue.
Any ideas?

I want to be able to pause a block in place when I click on it

Here is the website with the game/source code and want to try and see if i can pause a block as it falls when i left click it with my mouse but not sure the proper function for it. ( https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/By_example/Raining_rectangles )

You must clearTimeout() to make it paused, I have implemented a toggle on click of box i.e play/pause.
(function() {
"use strict"
window.addEventListener("load", setupAnimation, false);
var gl,
timer,
rainingRect,
scoreDisplay,
missesDisplay,
status,
paused = false;
function setupAnimation(evt) {
window.removeEventListener(evt.type, setupAnimation, false);
if (!(gl = getRenderingContext()))
return;
gl.enable(gl.SCISSOR_TEST);
rainingRect = new Rectangle();
timer = setTimeout(drawAnimation, 17);
document.querySelector("canvas")
.addEventListener("click", playerClick, false);
var displays = document.querySelectorAll("strong");
scoreDisplay = displays[0];
missesDisplay = displays[1];
status = displays[2];
}
var score = 0,
misses = 0;
function drawAnimation() {
gl.scissor(rainingRect.position[0], rainingRect.position[1],
rainingRect.size[0], rainingRect.size[1]);
gl.clear(gl.COLOR_BUFFER_BIT);
rainingRect.position[1] -= rainingRect.velocity;
if (rainingRect.position[1] < 0) {
misses += 1;
missesDisplay.innerHTML = misses;
rainingRect = new Rectangle();
}
// We are using setTimeout for animation. So we reschedule
// the timeout to call drawAnimation again in 17ms.
// Otherwise we won't get any animation.
timer = setTimeout(drawAnimation, 17);
}
function playerClick(evt) {
// We need to transform the position of the click event from
// window coordinates to relative position inside the canvas.
// In addition we need to remember that vertical position in
// WebGL increases from bottom to top, unlike in the browser
// window.
var position = [
evt.pageX - evt.target.offsetLeft,
gl.drawingBufferHeight - (evt.pageY - evt.target.offsetTop),
];
// if the click falls inside the rectangle, we caught it.
// Increment score and create a new rectangle.
var diffPos = [position[0] - rainingRect.position[0],
position[1] - rainingRect.position[1]
];
if (diffPos[0] >= 0 && diffPos[0] < rainingRect.size[0] &&
diffPos[1] >= 0 && diffPos[1] < rainingRect.size[1]) {
score += 1;
scoreDisplay.innerHTML = score;
// rainingRect = new Rectangle();
if (!paused) {
clearTimeout(timer)
paused = true;
status.innerHTML = 'Paused';
} else {
timer = setTimeout(drawAnimation, 17);
paused = false;
status.innerHTML = 'Playing';
}
}
}
function Rectangle() {
// Keeping a reference to the new Rectangle object, rather
// than using the confusing this keyword.
var rect = this;
// We get three random numbers and use them for new rectangle
// size and position. For each we use a different number,
// because we want horizontal size, vertical size and
// position to be determined independently.
var randNums = getRandomVector();
rect.size = [
5 + 120 * randNums[0],
5 + 120 * randNums[1]
];
rect.position = [
randNums[2] * (gl.drawingBufferWidth - rect.size[0]),
gl.drawingBufferHeight
];
rect.velocity = 1.0 + 6.0 * Math.random();
rect.color = getRandomVector();
gl.clearColor(rect.color[0], rect.color[1], rect.color[2], 1.0);
function getRandomVector() {
return [Math.random(), Math.random(), Math.random()];
}
}
function getRenderingContext() {
var canvas = document.querySelector("canvas");
canvas.width = canvas.clientWidth;
canvas.height = canvas.clientHeight;
var gl = canvas.getContext("webgl") ||
canvas.getContext("experimental-webgl");
if (!gl) {
var paragraph = document.querySelector("p");
paragraph.innerHTML = "Failed to get WebGL context." +
"Your browser or device may not support WebGL.";
return null;
}
gl.viewport(0, 0,
gl.drawingBufferWidth, gl.drawingBufferHeight);
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
return gl;
}
})();
<style>
body {
text-align: center;
}
canvas {
display: block;
width: 280px;
height: 210px;
margin: auto;
padding: 0;
border: none;
background-color: black;
}
button {
display: block;
font-size: inherit;
margin: auto;
padding: 0.6em;
}
</style>
<p>You caught
<strong>0</strong>.
You missed
<strong>0</strong>
Status
<strong>Playing</strong>.</p>
<canvas>Your browser does not seem to support
HTML5 canvas.</canvas>

As you can see in the code the function drawAnimation() is calling itself every 17ms using setTimeout() JavaScript function (and this is what creates steady animation).
function drawAnimation() {
.
.
.
timer = setTimeout(drawAnimation, 17);
}
In order to pause/stop the animation you would need to use JavaScript function clearTimeout(timer). Since you want to stop/pause the animation on click event you could just reuse the function playerClick (evt) { ... } from the code you already have and put the function clearTimeout(timer) there.
function playerClick (evt) {
.
.
.
clearTimeout(timer);
}
If you want to be able to continue with animation after you have paused it you'll need to implement some switch-logic (pause if it is already playing, play if it is already paused) inside your function playerClick (evt) or to use timers to continue the animation after some time, for example.

How to give transition effects to dynamically changing image backgrounds using JavaScript

I have a page wherein the background image for a particular div keeps changing dynamically. I wanna be able to give some transition effects on the images. The page runs on pure javascript. Here's my code:
var bgArray = ["images/1.jpg", "images/2.jpg", "images/3.jpg"];
var i = 0;
function myFunction() {
setInterval(function() {
if (i == 3) {
i = 0;
}
var urlString = bgArray[i];
var x = document.getElementById("myDiv");
x.style.background = "url(" + bgArray[i] + ") no-repeat";
x.style.backgroundSize = "1366px";
i = i + 1;
}, 6000);
}
myFunction();
Thank you.

#myDiv {
transition: background 1s;
}

HTML code
<div id = "myDiv"></div>
CSS code
#myDiv{
width: <yourDivWidth>;
height: <yourDivHeight>;
background-size: cover;
}
Javascript code
var box = document.getElementById("myDiv");
var imagesList = ["url('images/1.jpg')", "url('images/2.jpg')", "url('images/3.jpg')"];
i = 0;
box.style.backgroundImage = imagesList[i];
function nextImg(){
box.style.backgroundImage = imagesList[i+1];
//box.style.width = "1366px";
//box.style.height = "1366px";
//declare your width and height of div in css and give background-size: cover;.
i = i+1;
if(i == imagesList.length){
i = 0;
box.style.backgroundImage = imagesList[i];
}
}
window.onload = setInterval(nextImg, 6000);
Wait for 6 sec and see the background images changing.
If you want to set background image for the first 6sec also, then you can set that in your CSS.
Comment if u have any doubts.

onClick event on image while already moving

I'm trying to make an image that moves to the right on my website. When you click the image, it should move to the left. For now, this doesn't happen, any ideas? If possible, in pure Javascript and no Jquery ;)
Also, if you click the image for a second time, it should move to the right again. Every consecutive time, the image should move to the other side. I guess this would be best with a for-loop?
<script type"text/javascript">
window.onload = init;
var winWidth = window.innerWidth - movingblockobject.scrollWidth; //get width of window
var movingblock = null //object
movingblock.onclick = moveBlockLeft();
function init() {
movingblock = document.getElementById('movingblockobject'); //get object
movingblock.style.left = '0px'; //initial position
moveBlockRight(); //start animiation
}
function moveBlockRight() {
if (parseInt(movingblock.style.left) < winWidth) { // stop function if element touches max window width
movingblock.style.left = parseInt(movingblock.style.left) + 10 + 'px'; //move right by 10px
setTimeout(moveBlockRight,20); //call moveBlockRight in 20 msec
} else {
return;
}
}
function moveBlockLeft () {
movingblock.style.right = parseInt(movingblock.style.right) + 10 + 'px'
}
</script>

Please first go through the Basics of javascript before trying out something .
window.onload = init;
var winWidth = window.innerWidth;
var movingblock = null;
var intervalid = null;
var isLeft = false;
function init() {
console.log('Init');
movingblock = document.getElementById('movingblockobject');
movingblock.style.left = '0px';
intervalid = setInterval(function() {
moveBlock(true);
}, 2000);
movingblock.onclick = function() {
moveBlock(false);
};
}
function moveBlock(isSetInterval) {
if (!isSetInterval)
isLeft = !isLeft;
if (parseInt(movingblock.style.left) < winWidth) {
if (isLeft)
movingblock.style.left = parseInt(movingblock.style.left) - 10 + 'px';
else
movingblock.style.left = parseInt(movingblock.style.left) + 10 + 'px';
} else {
movingblock.style.left = '0px';
}
}
function moveBlockLeft() {
clearInterval(intervalid);
movingblock.style.right = parseInt(movingblock.style.right) + 10 + 'px';
intervalid = setInterval(moveBlockRight, 20);
}
<div id="movingblockobject" style="width:50px;height:50px;border:solid;position: absolute;">
var movingblock = null
this are mistakes you have delclared it as null and next line you are binding click event.Also for assigning click event you should assign the name of the function.
movingblock.onclick = moveBlockLeft;
above is basic bug there are lot like the above.I feel Self learning is much better for basics
try yourself.
try the above it will work but please try yourself

You should CSS3 transition, works like a charm. Just toggle a class "right"
HTML:
<html>
<head>
<style>
#movingblockobject{
width: 40px;
padding: 10px;
position: fixed;
height:10px;
left:0px;
-webkit-transition: left 2s; /* For Safari 3.1 to 6.0 */
transition: left 2s;
}
#movingblockobject.right{
left:200px;
}
</style>
<script src="http://code.jquery.com/jquery-1.11.1.min.js"></script>
<script>
$( document ).ready(function() {
$('#movingblockobject').on('click', function (e) {
$('#movingblockobject').toggleClass("right");
});
});
</script>
</head>
<body>
<div id="movingblockobject" class="demo">add image here</div>
</body>
</html>

Image() onLoad not waiting for image to load

I've figured out the centering and resizing issues, but I still can't get onLoad to work properly. Anyone have any ideas? I thought onLoad was supposed to wait for the image to be loaded completely before firing the code. As this is right now, it resizes the img for the next img, and fades it in before it's loaded, so the previous image fades in again. Once the show has run through once, it works perfectly, so obviously it's not waiting for the image to load completely before firing imageLoad().
<div id="slideShow">
<div id="slideShowImg" style="display:none; margin-right:auto; margin-left:auto;">
</div>
<div id="slideShowThumbs">
</div>
<script type="text/javascript">
loadXMLDoc('http://www.thehoppr.com/hopspots/82/82.xml', function() {
var slideShow = document.getElementById('slideShow');
var items = [];
var nl = xmlhttp.responseXML.getElementsByTagName('image');
var i = 0;
var t;
var slideShowImg = document.getElementById('slideShowImg');
var slideShow = document.getElementById('slideShow');
var maxHeight = 300;
var maxWidth = 800;
var imgNode = new Image();
function image() {
var nli = nl.item(i);
var src = nli.getAttribute('src').toString();
var width = parseInt(nli.getAttribute('width').toString());
var height = parseInt(nli.getAttribute('height').toString());
imgNode.onLoad = imageLoad();
imgNode.src = src;
imgNode.height = height;
imgNode.width = width;
imgNode.setAttribute("style", "margin-right:auto; margin-left:auto; display:block;");
var ratio = maxHeight / maxWidth;
if (imgNode.height / imgNode.width > ratio) {
// height is the problem
if (imgNode.height > maxHeight) {
imgNode.width = Math.round(imgNode.width * (maxHeight / imgNode.height));
imgNode.height = maxHeight;
}
} else {
// width is the problem
if (imgNode.width > maxHeight) {
imgNode.height = Math.round(imgNode.height * (maxWidth / imgNode.width));
imgNode.width = maxWidth;
}
}
}
function imageLoad() {
slideShowImg.appendChild(imgNode);
Effect.Appear('slideShowImg', {
duration: 1
});
t = setTimeout(nextImage, 7000);
}
function nextImage() {
slideShowImg.setAttribute("style", "display:none");
if (i < nl.length - 1) {
i++;
image();
} else {
i = 0;
image();
}
}
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
//XML Loaded, create the slideshow
alert(xmlhttp.responseText);
image();
}
});
</script>

Here are some of my thoughts (it's all open discussion)...
Preloading - Since you're limited to downloading 2 resources in parallel per hostname, it may not make sense to preload everything up front. Since it's a slideshow, how about modifying image() to download the i + 1 image through an Image object that doesn't get appended to the DOM? It doesn't seem beneficial to prefetch i + 2 and beyond in a slideshow setting.
Centering the images - Regarding using the auto margin width for horizontal centering, I believe you'll have to explicitly set the image to display:block. Obviously that doesn't solve centering vertically. Are all the images the same size? Also, will the slideShowImg div have a defined height/width? If so, then some math can be applied to achieve the centering.
Hope this helps! :)

Ok so I fixed the issue with the onLoad, and I even added a little preloading to help the slideshow along as well. All I had to do was define the onload first, and then do everything else except define the src inside the onload's function. I then added a little nextImg preloading so there's little if no hiccup between images even if it's the first time the browser is loading them. Here's the final code for anyone who has similar onload issues and finds there way here:
<div id="slideShow">
<div id="slideShowImg" style="display:none; margin-right:auto; margin-left:auto;">
</div>
<div id="slideShowThumbs">
</div>
<script type="text/javascript">
loadXMLDoc('/82.xml', function() {
var slideShow = document.getElementById('slideShow');
var items = [];
var nl = xmlhttp.responseXML.getElementsByTagName('image');
var i = 0;
var t;
var slideShowImg = document.getElementById('slideShowImg');
var slideShow = document.getElementById('slideShow');
var maxHeight = 300;
var maxWidth = 800;
var curImg = new Image();
var nextImg = new Image();
function image() {
var cli = nl.item(i);
var src = cli.getAttribute('src').toString();
var width = parseInt(cli.getAttribute('width').toString());
var height = parseInt(cli.getAttribute('height').toString());
curImg.onload = function() {
curImg.height = height;
curImg.width = width;
curImg.setAttribute("style", "margin-right:auto; margin-left:auto; display:block;");
slideShowImg.appendChild(curImg);
var ratio = maxHeight / maxWidth;
if (curImg.height / curImg.width > ratio) {
// height is the problem
if (curImg.height > maxHeight) {
curImg.width = Math.round(curImg.width * (maxHeight / curImg.height));
curImg.height = maxHeight;
}
} else {
// width is the problem
if (curImg.width > maxHeight) {
curImg.height = Math.round(curImg.height * (maxWidth / curImg.width));
curImg.width = maxWidth;
}
}
}
curImg.src = src;
if (i < nl.length - 1) {
var nli = nl.item(i + 1);
var nsrc = nli.getAttribute('src').toString();
nextImg.src = nsrc;
}
Effect.Appear('slideShowImg', {
duration: 1
});
t = setTimeout(nextImage, 7000);
}
function imageLoad() {}
function nextImage() {
slideShowImg.removeChild(curImg);
slideShowImg.setAttribute("style", "display:none");
if (i < nl.length - 1) {
i++;
image();
} else {
i = 0;
image();
}
}
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
//XML Loaded, create the slideshow
alert(xmlhttp.responseText);
image();
}
});
</script>