Develop Reference

Preloading Images in JavaScript (Need an Alert When Completed)

I have the following code below, which successfully preloads images into the browser cache when the PreloadAllImages function is called. Does anyone know how to send a simple alert, e.g. "All images have been preloaded into the browser cache." when the last image (or all images) is loaded. I have 300 images, so setTimeOut won't work for latency/download lag reasons. I've tried callbacks, placing alert commands in different places, etc... but have not been successful.
This code is based on JavaScript Only Method #1 found here. https://perishablepress.com/3-ways-preload-images-css-javascript-ajax/
function PreLoadAllImages() {
var images = new Array();
function preload() {
for (i = 0; i < preload.arguments.length; i++) {
images[i] = new Image();
images[i].src = preload.arguments[i];
}
}
preload('Images/Image1.jpg', 'Images/Image2.jpg', ... , 'Images/Image300.jpg');
}

With some help, this is how the problem was solved in case anyone else needs it. Loaded images into an invisible div on the html page, then ran script to ensure everything was loaded. A button calls PreLoadAllImages() and then CheckImages().
var imagefiles = [
"Images/Image1.jpg",
"Images/Image2.jpg",
.....
"Images/Image300.jpg"];
function PreLoadAllImages () {
imagefiles.forEach(function(image){
var img = document.createElement('img');
img.src = image;
document.body.appendChild(img);});
$('img').hide();
}
var all_loaded;
function CheckImages() {
$('img').each(function(){ // selecting all image element on the page
var img = new Image($(this)); // creating image element
img.src = $(this).attr('src'); // pass src to image object
if(img.complete==false) {
all_loaded=false;
return false;
}
all_loaded=true;
return true;});
}
function CheckLoadingImages() {
var result;
var Checking=setInterval(function(){
result=CheckImages();
if(all_loaded==true) {
clearInterval(Checking);
MsgAfterLoading();
}
}, 2000);
}
function MsgAfterLoading() {
alert('All Images Loaded');
}

You could check if i is equals to the length of the array, so it will look like:
for (i = 0; i < preload.arguments.length; i++) {
images[i] = new Image()
images[i].src = preload.arguments[i]
//the code
if (i == preload.arguments.length){
alert("Last image loaded");
}
//the code
}
Let me know if you have any questions.
Could you try looping through all the image elements and check the naturalWidth property, if they are all greater than 0 and its the last image then alert.
This link: Preloading Images in JavaScript (Need an Alert When Completed) should help

A promise might resolve your problem.
https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Promise
var myPromise = new Promise( function(resolve, reject) {
// preload code
resolve(true);
};
myPromise.then(function() {
// your alert
};

You can use the onload event.
function PreLoadAllImages() {
var images = new Array();
var numberofimages = 0, loadedimages = 0;
function preload() {
numberofimages = preload.arguments.length;
for (i = 0; i < preload.arguments.length; i++) {
images[i] = new Image();
images[i].src = preload.arguments[i];
images[i].onload = () => {
loadedimages++;
if(loadedimages == numberofimages){
alert("All images are loaded");
}
}
}
}
preload('Images/Image1.jpg', 'Images/Image2.jpg', ... , 'Images/Image300.jpg');
}

JS onclick Event Handler - Not Responding

What I'm trying to achieve: clicking on any image should either reveal a clear image if image is blurred or blur the image if image is clear
What's happening: clicking on blurred image clears the image, but clicking on it again does nothing. so, clicking on a clear image does not blur it (as it should).
Here's my code:
<script>
window.onload = init;
function init(e) {
var img = document.getElementsByTagName("img");
//var img = document.getElementById('pics');
img[0].onclick = unblur; // <- why not just img.onclick = unblur ??
img[1].onclick = unblur;
img[2].onclick = unblur;
console.log(img);
/*
var imageId = e.target.id; //zero
var img = document.getElementById(imageId);
*/
//img.onclick = unblur;
}
function unblur(e) {
var imageId = e.target.id; //zero
var img = document.getElementById(imageId);
var imageSource = img.src; //zeroblur.jpg
var clearImg = imageSource.substring(0, imageSource.length - 8);
var unblurredImg = imageId.concat('.jpg'); // zero.jpg
var blurredImg = imageId.concat('blur.jpg'); // zeroblur.jpg
console.log(imageSource);
console.log(img.src);
//console.log(imageSource);
if (img.src == unblurredImg) {
img.src = blurredImg;
} else {
img.src = unblurredImg; // image is clear, so hide the pic
}
/*
if (img.src == blurredImg) {
img.src = unblurredImg;
}
} */
//}
}
/*
//if (!(imageId instanceof img)) {
if (imageId !== "pics") {
if (img.src == blurredImg) {
img.src = unblurredImg;
} else if (img.src == unblurredImg) {
img.src = blurredImg;
} // image is blurred, so reveal the pic
else {
console.log("hi");
}
//debugger;
}
}
*/
/*
var img = document.getElementById('zero');
img.src = "zero.jpg";
*/
</script>
</head>
<body>
<div id="pics">
<img id="zero" src="zeroblur.jpg">
<img id="one" src="oneblur.jpg">
<img id="two" src="two.jpg">
</div>
</body>
</html>
I also noticed that if I switch the conditions in the function, unblur(e), to the following...
if (img.src == unblurredImg) {
img.src = blurredImg;
} else {
img.src = unblurredImg;
}
there's no response at all if a user clicks on a blurred image, whereas before (code above) the blurred image will at least reveal the cleared image.
Why is this happening? I see no difference between the two, besides just switching the order of the conditions.

There are various mistakes in your example. Take a look at the Code Snippet for a working example of what you are trying to achieve.
As for your comment:
// <- why not just img.onclick = unblur ??
Because document.getElementsByTagName returns an array of elements. Therefore, you must iterate through the elements to apply the onclick handlers to each one.
(function(document) {
var array = document.getElementsByTagName("img");
for (var i = 0; i < array.length; i++) {
array[i].onclick = toggleBlur;
}
function toggleBlur(event) {
var img = event.target;
var oldSrc = img.src; // Save to display in the console
if (img.src.endsWith("blur.jpg")) {
img.src = img.id + ".jpg";
} else {
img.src = img.id + "blur.jpg"
}
console.log(oldSrc + " -> " + img.src + " on element.id=" + img.id);
}
})(document);
<body>
<div id="pics">
<img id="zero" src="zero.jpg">
<img id="one" src="one.jpg">
<img id="two" src="twoblur.jpg">
</div>
</body>

Random image appear when website is loaded

I have 2 pictures for my website, and i want it to load one of them whem the website loads.
I have tried using some javascript. But i am quite new to all this.
This is how i am think i want to make it.
<div class="image">
Show one of 2 images here.
</div>
<script>
var r = Math.floor(Math.random() * 100) + 1;
if(r < 51) {
SHOW IMAGE 1
}
else {
SHOWIMAGE 2
}
</sccript>
So i was hoping someone could teach me how to actually turn this into functional code.
Thanks.

You can set the src attribute of an image directly using javascript, then use Math.random like you expected to pick between different image urls.
With an image tag with id 'random_image':
// images from wikipedia featured images/articles 2015-03-03
var img = document.getElementById('random_image');
if (Math.random() > .5) {
img.src = 'http://upload.wikimedia.org/wikipedia/en/thumb/4/45/Bradford1911.jpg/266px-Bradford1911.jpg';
} else {
img.src = 'http://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Pitta_sordida_-_Sri_Phang_Nga.jpg/720px-Pitta_sordida_-_Sri_Phang_Nga.jpg';
}
Here is a jsfiddle example: http://jsfiddle.net/8zd5509u/

1.way:
var _img = document.getElementById('id1');
var newImg = new Image;
newImg.onload = function() {
_img.src = this.src;
}
newImg.src = 'http://www.something.blabla.....';
another:
function preload(images) {
if (document.images) {
var i = 0;
var imageArray = new Array();
imageArray = images.split(',');
var imageObj = new Image();
for(i=0; i<=imageArray.length-1; i++) {
//document.write('<img src="' + imageArray[i] + '" />');// Write to page (uncomment to check images)
imageObj.src=imageArray[i];
}
}
}
Then in the of each web page, add the following code after you've called the main JavaScript file:
<script type="text/javascript">
preload('image1.jpg,image2.jpg,image3.jpg');
</script>

JS basic random image select

I've only started HTML yesterday and I'm trying to do a really basic memory game. First, there's an image of all the pieces, then a button that calls a function that hides that image and make another appear. This second image is a blank page with the spaces where the parts of the former image were. Also, there's an usemap and a function that returns if the player has clicked correctly or not. My problem is to come up with a function (and how to call it) to select a random part of the image.
function checkAnswer(a) {
if (a=='6') {
alert('Correct!')
}
else {
alert('Wrong!')
}
}
The 'a' must be a random number and follow the index of the chosen picture.
This is what I've found, but couldn't use:
<!-- Attempt of random
function random_imglink() {
var cobras=new Array()
cobras[1]="<img src ="..\images\Cobra1.jpg">"
cobras[2]="..\images\Cobra2.jpg"
cobras[3]="..\images\cobra3.jpg"
cobras[4]="..\images\cobra4.jpg"
cobras[5]="..\images\cobra5.jpg"
cobras[6]="..\images\cobra6.jpg"
cobras[7]="..\images\cobra7.jpg"
cobras[8]="..\images\cobra8.jpg"
cobras[9]="..\images\cobra9.jpg"
cobras[10]="..\images\cobra10.jpg"
cobras[11]="..\images\cobra11.jpg"
cobras[12]="..\images\cobra12.jpg"
cobras[13]="..\images\cobra13.jpg"
cobras[14]="..\images\cobra14.jpg"
cobras[15]="..\images\cobra15.jpg"
var ry=Math.floor(Math.random()*cobras.length)
if (ry=='0') {
ry = '1'
}
document.write('<img src="'+myimages[ry]+'" border=0>')
}
-->
<!-- Attempt of random
<script>
var imgArray = new Array();
imgArray[0] = new Image();
imgArray[0].src = '..\images\Cobra1.jpg';
imgArray[1] = new Image();
imgArray[1].src = '..\images\Cobra2.jpg';
imgArray[2] = new Image();
imgArray[2].src = '..\images\cobra3.jpg';
function nextImage(element)
{
var img = document.getElementById(element);
for(var i = 0; i < imgArray.length;i++)
{
if(imgArray[i].src == img.src)
{
if(i === imgArray.length){
document.getElementById(element).src = imgArray[0].src;
break;
}
document.getElementById(element).src = imgArray[i+1].src;
break;
}
}
}
</script>

Generic Javascript Image Swap

I'm building a navigation bar where the images should be swapped out on mouseover; normally I use CSS for this but this time I'm trying to figure out javascript. This is what I have right now:
HTML:
<li class="bio"><img src="images/nav/bio.jpg" name="bio" /></li>
Javascript:
if (document.images) {
var bio_up = new Image();
bio_up.src = "images/nav/bio.jpg";
var bio_over = new Image();
bio_over.src = "images/nav/bio-ov.jpg";
}
function over_bio() {
if (document.images) {
document["bio"].src = bio_over.src
}
}
function up_bio() {
if (document.images) {
document["bio"].src = bio_up.src
}
}
However, all of the images have names of the form "xyz.jpg" and "xyz-ov.jpg", so I would prefer to just have a generic function that works for every image in the navbar, rather than a separate function for each image.

A quick-fire solution which should be robust enough provided all your images are of the same type:
$("li.bio a").hover(function() {
var $img = $(this).find("img");
$img[0].src = $img[0].src.replace(".jpg", "") + "-ov.jpg";
}, function() {
var $img = $(this).find("img");
$img[0].src = $img[0].src.replace("-ov.jpg", "") + ".jpg";
});

This should work will all image formats as long as the extension is between 2 and 4 characters long IE. png, jpeg, jpg, gif etc.
var images = document.getElementById('navbar').getElementsByTagName('img'), i;
for(i = 0; i < images.length; i++){
images[i].onmouseover = function(){
this.src = this.src.replace(/^(.*)(\.\w{2,4})$/, '$1'+'-ov'+'$2');
}
images[i].onmouseout = function(){
this.src = this.src.replace(/^(.*)-ov(\.\w{2,4})$/, '$1'+'$2');
}
}

Here's an idea in plain javascript (no jQuery):
function onMouseOverSwap(e) {
e.src = e.src.replace(/\.jpg$/", "-ov.jpg"); // add -ov onto end
}
function onMouseOutSwap(e) {
e.src = e.src.replace(/(-ov)+\.jpg$/, ".jpg"); // remove -ov
}