Develop Reference

Why is my div not updating when changing its class with JavaScript?

I currently have a div that's used to display and image via CSS.
For example:
HTML
<div id="myDiv" class="play"></div>
CSS
.play{background: url('../img/playIcon_black.png') no-repeat;}
This image appears as it should.
What I'm attempted to do is to change the image by changing the class (via JavaScript).
Example:
CSS
.pause{background: url('../img/pauseIcon_black.png') no-repeat;}
JavaScript
function myFunction() {
myDiv.className = "pause";
}
When I call myFunction() everything seems to work correctly with one exception. Occasionally the image does not update in the browser.
A few things to note:
I'm certain the function is being called correctly. If I put a console.log() statement within the function, it prints when it should. Additionally, if I inspect the element within the browser, the class is in fact changed to .pause
The image changes from the "play icon" to blank once the function is called, BUT upon hovering over the div the images then appears permanently.
This only seems to happen once the page is initially loaded. Meaning, I can only recreate the issue once upon refresh, then everything works correctly after that.
I have attempted to clear my cache but nothing seems to have changed.
(I'm not sure how relevant this is) I'm calling myFunction() via onended attribute of an audio tag.
For example:
<audio onended="myFunction()"></audio>
But I'm not certain if this would affect anything because the function appears to be called correctly.
Any ideas of why this might be happening?

So the issue is that when you change the class, the browser has to fetch the new image, which takes time. One way to fix the issue is by using sprites, where both images are actually in one image and you only show a piece of that image at a time.
Another solution is to preload the image and then apply the preloaded image source to your new element like this:
var image = newImage();
image.src = '../img/pauseIcon_black.png';
function myFunction() {
var cssBackground = 'url(' + image.src + ') no-repeat';
myDiv.style.background = cssBackground;
// Optionally with jQuery instead:
// $('#myElementID').css('background', cssBackground);
}
Note that if you call myFunction before the image loads you'll encounter the same error. The difference is that this will load the image when the page is loaded (or more properly, when this JS executes and myFunction is assigned) rather than when myFunction is called. To ensure the image is loaded you can use the onLoad event handler for the image object. For more details on preloading images check out this answer: preload image then change background javascript

You need to get the element id
function myfunction(){
var myDivElem = document.getElementById('myDiv');
myDivElem.className = 'pause';
}

You can use document.getElementById("myDiv").className="";in your function
OK if you don't want use first solution you can use second one:
You can add a class to element using
document.getElementById("myDiv").className +=" n";
Then add a class named .play.n to your css file after class named.play
Then add your image address.

If you want to manipulate the div with id "myDiv". Use it as
document.getElementById('myDiv').class
Sample codesnippet: example snippet

Load a page via .load in pop-up

I'm trying to load a PHP page via jQuery. I want it to have a pop-up effect. I tried using the code below, but when the click event is triggered, it seems as if only the CSS from the imported page is being imported. The page content does not appear, but the look changes due to CSS conflicts.
I'd like the page to load and not conflict with the other CSS
function previewPop(){
$(".pop").click(function(){
$("iframe#preview").load("templates/1.php",
function(){$("iframe#preview").fadeIn(300); })
});
};

<div id="frame_wrapper">
</div>
$(".pop").click(function(){
var the_iframe = '<iframe id="my_iframe" src="' + templates/1.php + '" height="500px" width="500px">';
$('#frame_wrapper').append(the_iframe);
});
I hate dealing with iframes, so sometimes it's just easier to create a new one and destroy it as necessary.

How to insert a javascript file into an iframe then call a function in the inserted javascript?

Edit: Just found out this is a chrome problem, the code works fine in firefox
I have an iframe on a webpage that shows a book formatted as html. I would like to insert some javascript within this iframe to make the book more dynamic (e.g. click on sentences, show animations etc). The iframe content is in the same domain as the parent page.
I can insert the javascript into the iframe but get an error calling a function in the inserted javascript. I've described the different bits of code below:
My parent page javascript is:
function iframeLoaded()
{
var iFrameID = document.getElementById('preview-iframe');
var jsLink = iFrameID.contentDocument.createElement("script");
jsLink.src="/tests/iframeAPI.js";
jsLink.type = 'text/javascript';
iFrameID.contentDocument.head.appendChild(jsLink);
iFrameID.contentWindow.initialiseApi()
}
and the html containing the iframe is:
<iframe id="preview-iframe" width="640" height="240" frameborder="0" src="./testpage.htm" onload="iframeLoaded()" scrolling="no"></iframe>
The contents of iframeAPI.js is:
window.initialiseApi = function() { alert("Hello world") }
Looking at the iFrame's html in the browser shows that the iFrameAPI.js tag is inserted ok into the iframe head, but I don't get the alert popup when the page is loaded. The error appears on the following line:
iFrameID.contentWindow.initialiseApi()
Uncaught TypeError: Object [object Window] has no method 'initialiseApi'
However I can run this line in the browser's javascript console and the alert popup works fine.
Any help would be much appreciated.
Thanks,
Brian
Edit: I've just tried with an onload event to make sure the page is loaded and I still have the problem:
My parent page javascript is now :
function iframeLoaded()
{
var iFrameID = document.getElementById('preview-iframe');
var jsLink = iFrameID.contentDocument.createElement("script");
jsLink.src="/tests/iframeAPI.js";
jsLink.type = 'text/javascript';
iFrameID.contentDocument.head.appendChild(jsLink);
jsLink.onLoad= iFrameLoaded();
}
function iFrameLoaded()
{
alert("Iframe loaded"); // Alert works ok
var iFrameID = document.getElementById('preview-iframe');
iFrameID.contentWindow.initialiseApi(); // Same error message on this line
}

It sounds like you are trying to use the function before the content has loaded.
try this instead:
var t = setTimeout(iFrameID.contentWindow.initialiseApi(),500);
This will wait half a second before trying the function which should give the page tiem to load. Delay times are given in milliseconds.
An even better approach is to try using Jquery and its ready() method but this requires the jquery library to be loaded as well. Its well worth it though in my opinion, see http://api.jquery.com/ready/.
You would try something like:
$("body",iFrameID.contentWindow.document).ready(iFrameID.contentWindow.initialiseApi())

You're executing it right away without giving the script a chance to load. Hook up an onload event to your script block and run your main function then.

Try, in the page included in the iFrame, accessing the main page by doing something like:
window.parent.xyz = something;
Where something is what you want exposed to the main page. Could be a function or an object of functions. Now in the main page you can just do:
something(); // or something.somefunction();
You could also send window references, I think, but I have not tried that.

The easiest way is to call the initialiseApi function in the iframeAPI.js itself as it will be called as soon as it's loaded. The iframeAPI.js could look like that:
function initialiseApi() {
alert("Hello world");
}
initialiseApi();
There is no callback or timeout needed.

Javascript replace( ) function running more than once on the same image

I'm running a Javascript replace function to replace standard images with class="replace-2x"on my jQuery Mobile site with Retina-quality images if the user is on a mobile device with Retina display. For example, on a Retina device, logo.png will be replaced with logo#2x.png. The JS function is here:
function highdpi_init() {
$(".replace-2x").each(function () {
var src = $(this).attr("src");
$(this).attr("src", src.replace(".png", "#2x.png").replace(".jpg", "#2x.jpg"));
});
}
$(".page").live('pageinit',function(event){
highdpi_init();
});
I'm now running into an issue where the replace function is running more than once. So for example, it replaces logo.png with logo#2x.png as the page is loading, but then as the page continues to load, it KEEPS replacing .png with #2x.png in the img src over and over so that the image tag ends up looking like this:
<img src="mobile/images/logo#2x#2x#2x#2x#2x#2x#2x#2x#2x#2x#2x.png" class="replace-2x" alt="logo" width="200">
How can I prevent this from replacing on a single img element more than once? Keep in mind, I will have multiple images on the same page, so the function will need to apply to all images, but only one time each.

The problem is surely that your 'pageinit' event is being called more than once. You can either follow MДΓΓ БДLL's idea (which won't work if images are dynamically added) or you can make your handler smarter so that it doesn't replace the src if it already was replaced
function highdpi_init() {
$(".replace-2x").each(function () {
var $this = $(this);
var src = $this.attr("src");
$this.attr("src", src.replace(".png", "#2x.png").replace(".jpg", "#2x.jpg"));
// Remove the class so it doesn't replace it again
$this.removeClass('replace-2x')
});
}
You don't need JS for this, you could do it in CSS only.
<link rel="stylesheet" media="only screen and (-webkit-min-device-pixel-ratio: 2)" href="/css/highdpi.css"/>
You could make your images look like
<img src="transparent.gif" class="logo-a" alt="logo" width="200" />
And in highdpi.css you could do
img.logo-a {
background-image: url('file#2x.png')
}
And in lowdpi.css
img.logo-a {
background-image: url('file.png')
}

Using .one() should work since it is just a binding and if you are using Jquery Mobile the way that is suggested it will be just fine. That is unless you are passing back the html from the server. In which case it would be a good idea to add an extra condition to make sure that the src doesn't already have #2x.png before replacing.

There is disappointingly little documentation on pageinit on the offical jQuery Mobile docs. So I'm going to speculate here. It looks like pageinit is used to fire events for when a specific DOM element has finished loading, since it may not have been loaded on the initial page load (deferred until needed). That being said, it may be that adding/altering images to the DOM element in question fires the pageinit again. Could you tag each updated image with something that says, 'hey, I've already been updated to 2x'? Something such as
$.data(targetimg, 'retinafied', true);
And then check for that value before replacing the src?

Pre Load images to display later on click event jQuery

I have a web page where lots of images called from server using image
scr attribute.
I have created a function like which is triggered by td click.
function GoToStep(stepNo) {
var imgSrc = $("#h1" + stepNo).val();
$(".img_vertical").css("background-image", "url(" + imgSrc + ")");
}
Now the problem is this. For slower connections the images come after some
moment.
Can I pre load images to avoid waiting time when user clicks
td?
I have seen some jquery function to pre load images.
Kindly give some idea how can I achieve it.

Pre-loading an image is equivalent to loading an image but never displaying it. So, you can easily do it like this:
<img src="image.png" alt="" style="display:none;"/>
Now this image will be loaded as soon as the html starts rendering. Whenever you need to use this image as a display or background, just set the address to image.png and it will automatically be fetched from browser's cache.

This can be done using some javascript functions. Quoting from another question.
function preload(arrayOfImages) {
$(arrayOfImages).each(function(){
$('<img/>')[0].src = this;
// Alternatively you could use:
// (new Image()).src = this;
});
}
// Usage:
preload([
'img/imageName.jpg',
'img/anotherOne.jpg',
'img/blahblahblah.jpg'
]);
Explanation of how javascript preloaders work (different question)
[...] The way it works is simply by creating a new Image object and setting
the src of it, the browser is going to go grab the image. We're not
adding this particular image to the browser, but when the time comes
to show the image in the page via whatever method we have setup, the
browser will already have it in its cache and will not go fetch it
again. [...]
So in your case, you should use something like
$(function() {
// Do stuff when DOM is ready
preload([
'img/bg1.jpg',
'img/bg2.jpg',
'img/bg3.jpg'
]);
});