Develop Reference

Slideshow with timer

I was wondering if there was anyway to make a slideshow of images with a countdown timer on the slideshow.
I am making an exercise app, and need a course option. On the course option it is going to show an exercise for 20 seconds, then rest for 10 seconds etc. until the end of the course.
I have all the exercises ready, in images. I just need a code to show an image slideshow, with a countdown timer with it.
Thanks!

Slideshow with a timer would be using a setInterval() method. Try this:
<img src="some_source/to/file.png" alt="text" />
Then you can run a function to change its src attribute as
setInterval(changeAttr, 20000);
function changeAttr() {
$('img').attr('src', 'next_image.png');
}
You can use an if else block to change the image something like:
if($('img').attr('src') == 'some_image_file.png') {
$('img').attr('src', 'new_image_file.png');
}
Now the timer would execute each 20 seconds and will change the image's source attribute. It will use an if else block to determine which image to be set as the slideshow image.

Animated gifs not restarting in Firefox (with examples)

Description of Problem:
Animated gifs don't appear to restart properly in Firefox under many circumstances. This is an issue I only experience in Mozilla and with no other browser.
For example, why does this work to always restart it, but this does not? In the latter, the gif is clearly cached and looping forever in the background, so when you call .show() it will appear at some random point in the middle of the animation.
How can I achieve what I'm attempting to do in the second Fiddle and force the gif to restart each time I hide it? And no, I don't want to redownload the entire gif every single time, so appending '?random=' + Date.now() to the image is not a solution.
Code from Link #1:
$('#still, #animated').click(function() {
animated.attr('src', "");
animated.attr('src', srcToGif);
});
Code from Link #2:
$('#still, #animated').click(function() {
if (!clicked) {
clicked = 1;
animated.attr('src', "");
animated.attr('src', srcToGif);
animated.show();
setTimeout(function() {
animated.hide();
clicked = 0;
}, 9500);
}
});

Replace
animated.attr('src', "");
with
animated.removeAttribute('src');
Works for me in Firefox 30.
Assuming the word animated is a normal, non-jquery-specific img reference.
I don't do js libraries in general because I want to have control. The minification is often illusory due to the bulk of the library and when a quirk does occur, it's hard to troubleshoot.

Placeholder while an image is loading with Ember.js [duplicate]

I'm currently working on a web application which has a page which displays a single chart (a .png image). On another part of this page there are a set of links which, when clicked, the entire page reloads and looks exactly the same as before except for the chart in the middle of the page.
What I want to do is when a link is clicked on a page just the chart on the page is changed. This will speed things up tremendously as the page is roughly 100kb large, and don't really want to reload the entire page just to display this.
I've been doing this via JavaScript, which works so far, using the following code
document.getElementById('chart').src = '/charts/10.png';
The problem is that when the user clicks on the link, it may take a couple of seconds before the chart changes. This makes the user think that their click hasn't done anything, or that the system is slow to respond.
What I want to happen is display a spinner / throbber / status indicator, in place of where the image is while it is loading, so when the user clicks the link they know at least the system has taken their input and is doing something about it.
I've tried a few suggestions, even using a psudo time out to show a spinner, and then flick back to the image.
A good suggestion I've had is to use the following
<img src="/charts/10.png" lowsrc="/spinner.gif"/>
Which would be ideal, except the spinner is significantly smaller than the chart which is being displayed.
Any other ideas?

I've used something like this to preload an image and then automatically call back to my javascript when the image is finished loading. You want to check complete before you setup the callback because the image may already be cached and it may not call your callback.
function PreloadImage(imgSrc, callback){
var objImagePreloader = new Image();
objImagePreloader.src = imgSrc;
if(objImagePreloader.complete){
callback();
objImagePreloader.onload=function(){};
}
else{
objImagePreloader.onload = function() {
callback();
// clear onLoad, IE behaves irratically with animated gifs otherwise
objImagePreloader.onload=function(){};
}
}
}

You could show a static image that gives the optical illusion of a spinny-wheel, like these.

Using the load() method of jQuery, it is easily possible to do something as soon as an image is loaded:
$('img.example').load(function() {
$('#spinner').fadeOut();
});
See: http://api.jquery.com/load-event/

Use the power of the setTimeout() function (More info) - this allows you set a timer to trigger a function call in the future, and calling it won't block execution of the current / other functions (async.).
Position a div containing the spinner above the chart image, with it's css display attribute set to none:
<div> <img src="spinner.gif" id="spinnerImg" style="display: none;" /></div>
The nbsp stop the div collapsing when the spinner is hidden. Without it, when you toggle display of the spinner, your layout will "twitch"
function chartOnClick() {
//How long to show the spinner for in ms (eg 3 seconds)
var spinnerShowTime = 3000
//Show the spinner
document.getElementById('spinnerImg').style.display = "";
//Change the chart src
document.getElementById('chart').src = '/charts/10.png';
//Set the timeout on the spinner
setTimeout("hideSpinner()", spinnerShowTime);
}
function hideSpinner() {
document.getElementById('spinnerImg').style.display = "none";
}

Use CSS to set the loading animation as a centered background-image for the image's container.
Then when loading the new large image, first set the src to a preloaded transparent 1 pixel gif.
e.g.
document.getElementById('mainimg').src = '/images/1pix.gif';
document.getElementById('mainimg').src = '/images/large_image.jpg';
While the large_image.jpg is loading, the background will show through the 1pix transparent gif.

Building on Ed's answer, I would prefer to see something like:
function PreLoadImage( srcURL, callback, errorCallback ) {
var thePic = new Image();
thePic.onload = function() {
callback();
thePic.onload = function(){};
}
thePic.onerror = function() {
errorCallback();
}
thePic.src = srcURL;
}
Your callback can display the image in its proper place and dispose/hide of a spinner, and the errorCallback prevents your page from "beachballing". All event driven, no timers or polling, plus you don't have to add the additional if statements to check if the image completed loading while you where setting up your events - since they're set up beforehand they'll trigger regardless of how quickly the images loads.

Some time ago I have written a jQuery plugin which handles displaying a spinner automatically http://denysonique.github.com/imgPreload/
Looking in to its source code should help you with detecting when to display the spinner and with displaying it in the centre of the loaded image.

I like #duddle's jquery method but find that load() isn't always called (such as when the image is retrieved from cache in IE). I use this version instead:
$('img.example').one('load', function() {
$('#spinner').remove();
}).each(function() {
if(this.complete) {
$(this).trigger('load');
}
});
This calls load at most one time and immediately if it's already completed loading.

put the spinner in a div the same size as the chart, you know the height and width so you can use relative positioning to center it correctly.

Aside from the lowsrc option, I've also used a background-image on the img's container.

Be aware that the callback function is also called if the image src doesn't exist (http 404 error). To avoid this you can check the width of the image, like:
if(this.width == 0) return false;

#iAn's solution looks good to me. The only thing I'd change is instead of using setTimeout, I'd try and hook into the images 'Load' event. This way, if the image takes longer than 3 seconds to download, you'll still get the spinner.
On the other hand, if it takes less time to download, you'll get the spinner for less than 3 seconds.

I would add some random digits to avoid the browser cache.

HTML / Javascript wait for graphics to be drawn

I've heard about the onload function which is called after the element is fully loaded.
In the case of graphics or images, does that mean it will wait until the image is displayed in the browser?
<body onload="foo()">...
<img onload="bar();"....
If not, is there a way to get the event when all graphics are drawn and images are displayed on a page?
In my case it´s only one 1600*1200 jpeg image and i draw on it. But the image has to be displayed before i start drawing, even with the onload event i see the drawed lines before the image appear.

Yes body onload will wait until all images (and other content) are loaded/displayed in the browser. The img onload will wait until that specific image has loaded/is displayed

Images have a complete property that's true when they are loaded.
e.g. would test if everything has loaded:
var allImagesLoaded = true;
$("IMG").each(function(){ allImagesLoaded &= $(this).attr("complete"); });
if(allImagesLoaded){ alert("Done!");}
Images raise a load event once they've finished loading

why dont you keep a counter for your images that will decrement by one on each image load.
check if it equal to 0 then call some another function.
in this way you can do the thing you want to when all images are loaded
$(function() {
$('img').one('load',function() {
// fire when image loads decrement the counter
if counter ==0
fireanotherfunction()
});
});
by above code u can attain your purpose

When reading the jQuery ready API documentation here:
While JavaScript provides the load event for executing code when a
page is rendered, this event does not get triggered until all assets
such as images have been completely received.
So onload is launched after everything has been loaded (and displayed).

See the window.load event:
The load event fires at the end of the document loading process. At this point, all of the objects in the document are in the DOM, and all the images and sub-frames have finished loading.
This is exact what you want, I believe.
JQuery's $(document).ready is not what you want:
In cases where code relies on loaded assets (for example, if the dimensions of an image are required), the code should be placed in a handler for the load event [instead of the ready event].
If you're using plain JS, window.load is what you want.
If you are using jQuery, you'll want $(document).load.

try jquery ready function
$(document).ready(function(){
bar();
});
I'm not sure if it works, but it's a try :D

I have the same problem developing a web view for an Android app. The load events (both for window and image element) as well as the complete state of the image element fire too early. My (svg) image has not yet finished drawing and thus calculations on the size go wrong.
The only workaround that I have found is a very short timer (1ms or maybe 10ms). That works for me because I have only one such image to consider. And since I start this timer when the image data has already loaded, this short lapse should be long enough for the device to paint the image.
window.addEventListener('load', function() {
var img = document.getElementById('logo');
window.setTimeout(function(){
var imgRatio = img.naturalWidth / img.naturalHeight;
var renderedWidth = parseInt(window.getComputedStyle(img).width.match(/(\d+)px/));
console.log(renderedWidth, img.complete);
if (renderedWidth < img.naturalWidth) {
img.style.height = (renderedWidth / imgRatio) + 'px';
}
}, 1);
}
Instead of the window load event, the image's load event should also work. But I found it safer to wait for everything, because other elements might affect the drawing of my image.

Setting GIF loop count and publishing stop event using JavaScript

Is it possible to set the loop count of a GIF image using JavaScript and then publish an event when it stops playing?
For example something like:
//html code
<img src="myImage.gif" id="img1"/>
//Javascript code
var image = document.getElementById('img1');
//Image must stop playing after 3 loops
image.setLoopCount = 3;

here is how i would suggest doing it:
extract frames form gif file (you can do it online using for instace -> http://imgops.com/)
use javascript to change pictures, simulating animation (that way you can keep track of how many loops you have done)
Here is a jsFiddle link http://jsfiddle.net/qustosh/n5zWH/9/
I used jQuery. I did three loops and i threw a callback function at the end.

For a design side solution, you can set the GIF image to only loop a certain number of times with Photoshop. Then just use window.setTimeout(callback, milliseconds) to trigger your custom event.
You can calculate the time out from the interval used to display each frame of the animation.