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Changing a picture by clicking on it with Javascript

This is my first ever question on here and I figure it must have a simple answer but it's frustrated me for a while, especially since I'm new to Javascript. So I have many images and would like to change to the next one by clicking on it on the webpage, starting with a certain image, obviously. Now I could do this with nested if else statements but if you have many images you get too many ones nested into each other and it can get too complex so I figured there must be a simpler way of doing it. Here's an example of the code I had:
function changeImage()
{
var image=document.getElementById("mainImage")
if (image.src.match("image1.jpg"))
{
image.src="image2.jpg";
}
else if (image.src.match("image2.jpg"))
{
image.src="image3.jpg";
}
else
{
if (image.src.match("image3.jpg"))
{
image.src="image4.jpg";
}
else
{
image.src="image1.jpg";
}
}
}
So you can see it's not the best way to do it. I tried to do it with a switch statement but I couldn't either (and would appreciate it if someone told me if it could be done with one and how). As a last try I tried this but for some reason it jumps from image1 to image4 at once:
function changeImage()
{
var images = ["image1.jpg", "image2.jpg", "image3.jpg", "image4.jpg"]
var myImage = document.getElementById("mainImage")
for (i=0; i < images.length; i++)
{
if (myImage.src.match(images[i]))
{
myImage.src = images[i+1]
}
}
}
So I could really appreciate some help. Thanks in advance.

Your last changeImage goes to #4 immediately because you're changing the image in the for loop which causes the check within the loop to keep being true and so it runs all the way to the last index, at which point the check finally fails. Instead, you'll want to maintain the current image index with a variable. Then, just change myImage.src to images[currentIndex + 1] on each click. Try something like below. You'll want to run showNextImage on page load and then run it once each time the image is clicked.
<script>
var currentImageIndex = 0;
//Cycle through images
showNextImage() {
var images = ["image1.jpg", "image2.jpg", "image3.jpg", "image4.jpg"]
var myImage = document.getElementById("mainImage")
myImage.src = images[currentImageIndex];
currentImageIndex++;
if(currentImageIndex >= images.length)
currentImageIndex = 0;
}
</script>

Why does this "loading message" script not work in FF?(javascript)

I have this script which should show the text "Loading..." while images are loading, then change the text to "loaded" when all images are loaded. I added a button to load new images to make sure that it works for dynamically loaded images as well.
This works perfectly in Chrome but in Firefox the "Loading..." text never appears. I have no idea why this would be. The page begins loading and not all images are loaded so it should create the text "Loading.." but it doesn't. Then when all images are done loading the text "Loading" appears.
I just don't get why one message would appear and the other wouldn't. Especially because there are no qualifications that have to be met before creating the "Loading..." text, it should just fire automatically.
jsfiddle Example | Full Page Example
$(document).ready(function() {
var checkComplete = function() {
if($('img').filter(function() {return $('img').prop('complete');}).length == $('img').length) {
$('.status').text('Loaded');
} else {
$('.status').text('Loading...');
}
};
$('img').on('load',function() {
checkComplete();
});
$('#button').click(function() {
$('img.a').attr('src' , 'http://farm9.staticflickr.com/8545/8675107979_ee12611e6e_o.jpg');
$('img.b').attr( 'src' , 'http://farm9.staticflickr.com/8382/8677371836_651f586c99_o.jpg');
checkComplete();
});
checkComplete();
});

You have several issues in the code.
First off, the checkComplete() function is not written correctly. It should be this:
var checkComplete = function() {
var imgs = $('img');
if(imgs.filter(function() {return this.complete;}).length == imgs.length) {
$('.status').text('Loaded');
} else {
$('.status').text('Loading...');
}
};
The main fix here is that the filter callback needs to refer to this.complete, not to $('img').prop('complete') because you are trying to filter a single item at a time.
Second off, you are relying on both .complete and .load working correctly AFTER you've changed the .src value. This is explicitly one of the cases where they do not work properly in all browsers.
The bulletproof way to work around this is to create a new image object for the new images, set the onload handler before you set the .src value and when both onload handlers have fired, you will know that both new images are loaded and you can replace the once you have in the DOM with the new ones.
Here is a version that works in FF:
$(document).ready(function() {
$('#button').click(function() {
var imgA = new Image();
var imgB = new Image();
imgA.className = "a";
imgB.className = "b";
var loaded = 0;
imgA.onload = imgB.onload = function() {
++loaded;
if (loaded == 2) {
$("img.a").replaceWith(imgA);
$("img.b").replaceWith(imgB);
$('.status').text('Loaded');
}
}
// the part with adding now to the end of the URL here is just for testing purposes to break the cache
// remove that part for deployment
var now = new Date().getTime();
imgA.src = 'http://farm9.staticflickr.com/8545/8675107979_ee12611e6e_o.jpg?' + now;
imgB.src = 'http://farm9.staticflickr.com/8382/8677371836_651f586c99_o.jpg?' + now;
$('.status').text('Loading...');
});
});
Working demo: http://jsfiddle.net/jfriend00/yy7GX/
If you want to preserve the original objects, you can use the newly created objects only for preloading the new images and then change .src after they've been preloaded like this:
$(document).ready(function() {
$('#button').click(function() {
var imgA = new Image();
var imgB = new Image();
var loaded = 0;
imgA.onload = imgB.onload = function() {
++loaded;
if (loaded == 2) {
$("img.a")[0].src = imgA.src;
$("img.b")[0].src = imgB.src;
$('.status').text('Loaded');
}
}
// the part with adding now to the end of the URL here is just for testing purposes to break the cache
// remove that part for deployment
var now = new Date().getTime();
imgA.src = 'http://farm9.staticflickr.com/8545/8675107979_ee12611e6e_o.jpg?' + now;
imgB.src = 'http://farm9.staticflickr.com/8382/8677371836_651f586c99_o.jpg?' + now;
$('.status').text('Loading...');
});
});
Working demo of this version: http://jsfiddle.net/jfriend00/ChSQ5/

From the jQuery API .load method
Caveats of the load event when used with images
A common challenge developers attempt to solve using the `.load()` shortcut is to execute a function when an image (or collection of images) have completely loaded. There are several known caveats with this that should be noted. These are:
It doesn't work consistently nor reliably cross-browser
It doesn't fire correctly in WebKit if the image src is set to the same src as before
It doesn't correctly bubble up the DOM tree
Can cease to fire for images that already live in the browser's cache

Jquery - Carasol build finished and would like advice on best practice / neatening up my code

I have been building my own carasol over the past few days.
My Jquery is based on tutorials on the web and also from help and advice from SO.
I am not a Jquery guru just an enthusiast and think my code is a little sloppy, hence the post.
here is a link to the working code: http://jsfiddle.net/JHqBA/2/ (updated link)
basically what happens is:
if someone hits the page with a # values in the url it will show the appropriate slide and example would be www.hello.com#two, this would slide to slide two
if someone clicks the numbers it will show the appropriate slide
next and prev also slide through the slides.
The question is, is there anything i could have wrote better as i know there is alot of duplicate code.
I understand its a big ask but it would help me learn a little more (i think my code is a little old school)
if anyone has any questions please feel free to ask and ill answer what it does or is supposed to do.
Sluap
--- Edit ----
I have made only one aniamtion function now which has got rid of alot of duplicate code.
I have yet to look into on function but will do soon.
I would like to know more about the create a new function, outside of the jQuery ready block as i cant get this working or quite understand how i can get it to work sorry
any more tips would be great ill carry on working on this project till i am happy with it.
also is there a better way to write:
if ($slideNumber == 1) {
$('#prev').attr("class", "not_active")
$('#next').attr("class", "active")
}
else if ($slideNumber == divSum) {
$('#next').attr("class", "not_active");
$('#prev').attr("class", "active");
}
else {
$('#prev').attr("class", "active")
$('#next').attr("class", "active")
};
Jquery full:
$(document).ready(function () {
//////////////////////////// INITAL SET UP /////////////////////////////////////////////
//Get size of images, how many there are, then determin the size of the image reel.
var divWidth = $(".window").width();
var divSum = $(".slide").size();
var divReelWidth = divWidth * divSum;
//Adjust the image reel to its new size
$(".image_reel").css({ 'width': divReelWidth });
//set the initial not active state
$('#prev').attr("class", "not_active");
//////////////////////////// SLIDER /////////////////////////////////////////////
//Paging + Slider Function
rotate = function () {
var triggerID = $slideNumber - 1; //Get number of times to slide
var image_reelPosition = triggerID * divWidth; //Determines the distance the image reel needs to slide
//sets the active on the next and prev
if ($slideNumber == 1) {
$('#prev').attr("class", "not_active")
$('#next').attr("class", "active")
}
else if ($slideNumber == divSum) {
$('#next').attr("class", "not_active");
$('#prev').attr("class", "active");
}
else {
$('#prev').attr("class", "active")
$('#next').attr("class", "active")
};
//Slider Animation
$(".image_reel").animate({
left: -image_reelPosition
}, 500);
};
//////////////////////////// SLIDER CALLS /////////////////////////////////////////////
//click on numbers
$(".paging a").click(function () {
$active = $(this); //Activate the clicked paging
$slideNumber = $active.attr("rel");
rotate(); //Trigger rotation immediately
return false; //Prevent browser jump to link anchor
});
//click on next button
$('#next').click(function () {
if (!$(".image_reel").is(':animated')) { //prevent clicking if animating
var left_indent = parseInt($('.image_reel').css('left')) - divWidth;
var slideNumberOn = (left_indent / divWidth);
var slideNumber = ((slideNumberOn * -1) + 1);
$slideNumber = slideNumber;
if ($slideNumber <= divSum) { //do not animate if on last slide
rotate(); //Trigger rotation immediately
};
return false; //Prevent browser jump to link anchor
}
});
//click on prev button
$('#prev').click(function () {
if (!$(".image_reel").is(':animated')) { //prevent clicking if animating
var left_indent = parseInt($('.image_reel').css('left')) - divWidth;
var slideNumberOn = (left_indent / divWidth);
var slideNumber = ((slideNumberOn * -1) - 1);
$slideNumber = slideNumber;
if ($slideNumber >= 1) { //do not animate if on first slide
rotate(); //Trigger rotation immediately
};
}
return false; //Prevent browser jump to link anchor
});
//URL eg:www.hello.com#one
var hash = window.location.hash;
var map = {
one: 1,
two: 2,
three: 3,
four: 4
};
var hashValue = map[hash.substring(1)];
//animate if hashValue is not null
if (hashValue != null) {
$slideNumber = hashValue;
rotate(); //Trigger rotation immediately
return false; //Prevent browser jump to link anchor
};
});

Question and answer has been moved over to https://codereview.stackexchange.com/questions/8634/jquery-carasol-build-finished-and-would-like-advice-on-best-practice-neateni/8635#8635
1) Separation of Concerns
Start by refactorring your code in to more granular functions.
You can read more about SoF at http://en.wikipedia.org/wiki/Separation_of_concerns
Update:
E.g. Instead of having your reel resizing code inline, put it in it's own function, like this:
function setImageReelWidth () {
//Get size of images, how many there are, then determin the size of the image reel.
var divWidth = $(".window").width();
var divSum = $(".slide").size();
var divReelWidth = divWidth * divSum;
//Adjust the image reel to its new size
$(".image_reel").css({ 'width': divReelWidth });
}
This achieves 2 things:
a. First, it groups a block of code that is logically cohesive, removing it from the main code which results in a much cleaner code habitat.
b. It effectively gives a label to the code block via the function name that is descriptive of what it does, and therefore makes understanding of the code much simpler.
Later, you can also encapsulate the whole thing in it's own "class" (function) and you can move it into it's own js file.
2) The jQuery "on" function
Use the "on" function to attach your click events, rather than the "click" function.
http://api.jquery.com/on/
This has the added advantage of also binding it to future elements matching your selector, even though they do not exist yet.
3) The ready function
// I like the more succinct:
$(handler)
// Instead of:
$(document).ready(handler)
But you might like the more obvious syntax.
Those are just a few things to start with.
-- Update 1 --
Ok, StackOverflow is not really suited to a refactoring work in progress, but we'll make do. I think you should keep your original code block in your question, so that future readers can see where it started and how it systematically improved.
I would like to know more about the create a new function, outside of
the jQuery ready block as i cant get this working or quite understand
how i can get it to work sorry
I am not familiar with jsfiddle.net, but it looks cool and helpful, but might also be a bit confusing if you don't know what is going on. I am not sure I do :), but I think that script editor window results in a .js file that is automatically referenced by the html file.
So here is an example of a function defined outside of the ready block, but referenced from within.
function testFunction () {
alert ('it works');
}
$(document).ready(function () {
testFunction();
// ... other code
});
This should pop up an alert box that says, "it works" when the page is loaded.
You can try it for yourself.
Then, once you got that working, you can refactor other logically cohesive blocks of code into their own functions. Later you can wrap them all up into their own javascript 'class'. But we'll get to that.

Can I optimise this js Prototype gallery to animate faster in IE?

I'm using a js image gallery on a magento site. Because Magento uses prototype, I've used prototype for this gallery; it's a simple application and I thought it unnecessary to load jQuery library as well just for this one element.
If you have a look at http://web74.justhost.com/~persia28/ in IE8 or less, the transitions between gallery slides is so slow, to the point where the text from one slide remains visible for a short time when the next slide is in place.
I know IE is rubbish with js, but I thought the extent of the slowness here is extreme, even for IE.
I don't want to load jQuery library just for this one gallery, Magento is enough of a tank as it is; so if it came to that I might opt for just putting the text in the images, not in HTML.
Anyway, would be great to hear your wisdom.
Many thanks, and here is the js code for the gallery.
var i = 0;
// The array of div names which will hold the images.
var image_slide = new Array('image-1', 'image-2', 'image-3');
// The number of images in the array.
var NumOfImages = image_slide.length;
// The time to wait before moving to the next image. Set to 3 seconds by default.
var wait = 4000;
// The Fade Function
function SwapImage(x,y) {
$(image_slide[x]).appear({ duration: 1.5 });
$(image_slide[y]).fade({duration: 1.5});
}
// the onload event handler that starts the fading.
function StartSlideShow() {
play = setInterval('Play()',wait);
$('PlayButton').hide();
$('PauseButton').appear({ duration: 0});
}
function Play() {
var imageShow, imageHide;
imageShow = i+1;
imageHide = i;
if (imageShow == NumOfImages) {
SwapImage(0,imageHide);
i = 0;
} else {
SwapImage(imageShow,imageHide);
i++;
}
}
function Stop () {
clearInterval(play);
$('PlayButton').appear({ duration: 0});
$('PauseButton').hide();
}
function GoNext() {
clearInterval(play);
$('PlayButton').appear({ duration: 0});
$('PauseButton').hide();
var imageShow, imageHide;
imageShow = i+1;
imageHide = i;
if (imageShow == NumOfImages) {
SwapImage(0,imageHide);
i = 0;
} else {
SwapImage(imageShow,imageHide);
i++;
}
}
function GoPrevious() {
clearInterval(play);
$('PlayButton').appear({ duration: 0});
$('PauseButton').hide();
var imageShow, imageHide;
imageShow = i-1;
imageHide = i;
if (i == 0) {
SwapImage(NumOfImages-1,imageHide);
i = NumOfImages-1;
} else {
SwapImage(imageShow,imageHide);
i--;
}
}

I looked at the site and it doesn't seem slow, it takes the same time to run. It looks as though the text is not changing in opacity until the end of the animation then is just being hidden. When I look with IE7 it works normally which is a clue, IE8 has a different way of making transparencies.
Magento still ships with Prototype 1.6.0 when I know that Prototype 1.6.1 fixes several IE8 bugs and Prototype 1.7 fixes some IE9 bugs too. You could try upgrading Prototype and Scriptaculous in the js/prototype/ and js/scriptaculous/ directories. I don't know if that exact problem is included which is why you should make a backup before overwriting files, if this doesn't work you will have something to rollback to.

How to improve image cross-fade performance?

I want to be able to do a cross fade transition on large images whose width is set to 100% of the screen. I have a working example of what I want to accomplish. However, when I test it out on various browsers and various computers I don't get a buttery-smooth transition everywhere.
See demo on jsFiddle: http://jsfiddle.net/vrD2C/
See on Amazon S3: http://imagefader.s3.amazonaws.com/index.htm
I want to know how to improve the performance. Here's the function that actually does the image swap:
function swapImage(oldImg, newImg) {
newImg.css({
"display": "block",
"z-index": 2,
"opacity": 0
})
.removeClass("shadow")
.animate({ "opacity": 1 }, 500, function () {
if (oldImg) {
oldImg.hide();
}
newImg.addClass("shadow").css("z-index", 1);
});
}
Is using jQuery animate() to change the opacity a bad way to go?

You might want to look into CSS3 Transitions, as the browser might be able to optimize that better than Javascript directly setting the attributes in a loop. This seems to be a pretty good start for it:
http://robertnyman.com/2010/04/27/using-css3-transitions-to-create-rich-effects/

I'm not sure if this will help optimize your performance as I am currently using IE9 on an amped up machine and even if I put the browser into IE7 or 8 document mode, the JavaScript doesn't falter with your current code. However, you might consider making the following optimizations to the code.
Unclutter the contents of the main photo stage by placing all your photos in a hidden container you could give an id of "queue" or something similar, making the DOM do the work of storing and ordering the images you are not currently displaying for you. This will also leave the browser only working with two visible images at any given time, giving it less to consider as far as stacking context, positioning, and so on.
Rewrite the code to use an event trigger and bind the fade-in handling to the event, calling the first image in the queue's event once the current transition is complete. I find this method is more well-behaved for cycling animation than some timeout-managed scripts. An example of how to do this follows:
// Bind a custom event to each image called "transition"
$("#queue img").bind("transition", function() {
$(this)
// Hide the image
.hide()
// Move it to the visible stage
.appendTo("#photos")
// Delay the upcoming animation by the desired value
.delay(2500)
// Slowly fade the image in
.fadeIn("slow", function() {
// Animation callback
$(this)
// Add a shadow class to this image
.addClass("shadow")
// Select the replaced image
.siblings("img")
// Remove its shadow class
.removeClass("shadow")
// Move it to the back of the image queue container
.appendTo("#queue");
// Trigger the transition event on the next image in the queue
$("#queue img:first").trigger("transition");
});
}).first().addClass("shadow").trigger("transition"); // Fire the initial event
Try this working demo in your problem browsers and let me know if the performance is still poor.

I had the same problem too. I just preloaded my images and the transitions became smooth again.

The point is that IE is not W3C compliant, but +1 with ctcherry as using css is the most efficient way for smooth transitions.
Then there are the javascript coded solutions, either using js straight (but need some efforts are needed to comply with W3C Vs browsers), or using libs like JQuery or Mootools.
Here is a good javascript coded example (See demo online) compliant to your needs :
var Fondu = function(classe_img){
this.classe_img = classe_img;
this.courant = 0;
this.coeff = 100;
this.collection = this.getImages();
this.collection[0].style.zIndex = 100;
this.total = this.collection.length - 1;
this.encours = false;
}
Fondu.prototype.getImages = function(){
var tmp = [];
if(document.getElementsByClassName){
tmp = document.getElementsByClassName(this.classe_img);
}
else{
var i=0;
while(document.getElementsByTagName('*')[i]){
if(document.getElementsByTagName('*')[i].className.indexOf(this.classe_img) > -1){
tmp.push(document.getElementsByTagName('*')[i]);
}
i++;
}
}
var j=tmp.length;
while(j--){
if(tmp[j].filters){
tmp[j].style.width = tmp[j].style.width || tmp[j].offsetWidth+'px';
tmp[j].style.filter = 'alpha(opacity=100)';
tmp[j].opaque = tmp[j].filters[0];
this.coeff = 1;
}
else{
tmp[j].opaque = tmp[j].style;
}
}
return tmp;
}
Fondu.prototype.change = function(sens){
if(this.encours){
return false;
}
var prevObj = this.collection[this.courant];
this.encours = true;
if(sens){
this.courant++;
if(this.courant>this.total){
this.courant = 0;
}
}
else{
this.courant--;
if(this.courant<0){
this.courant = this.total;
}
}
var nextObj = this.collection[this.courant];
nextObj.style.zIndex = 50;
var tmpOp = 100;
var that = this;
var timer = setInterval(function(){
if(tmpOp<0){
clearInterval(timer);
timer = null;
prevObj.opaque.opacity = 0;
nextObj.style.zIndex = 100;
prevObj.style.zIndex = 0;
prevObj.opaque.opacity = 100 / that.coeff;
that.encours = false;
}
else{
prevObj.opaque.opacity = tmpOp / that.coeff;
tmpOp -= 5;
}
}, 25);
}