Develop Reference

Jquery Check if image done loading

I'm using the following to refresh the images which i'm using to prevents bots. So i want to show some GIF while the image is loading and hide it when loading is done.
$.CaptchaLoad = function(){
var src = '../php/captcha.php',
stamp = (new Date()).getTime(),
url = src + '?' + stamp;
document.getElementById('capcha').src = url;
};
Is in Ajax where i would use 'Success';

I'm not sure what $.CaptchaLoad plugin?
if above code works fine in your case.
Add onload listener to image object.
$("#capcha").on("load",function(){
//successfully loaded
//write a code here to hide your loader.
});

You could try .load event.
$("#capcha").load(function(){
//hide your GIF
});
But notice that there are some Caveats of the load event when used with images, quoted from the doc:
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
One of them is : Can cease to fire for images that already live in the browser's cache. In your case, adding the timestamp does the trick. Remember not to remove it.

Determine when an image has loaded in svg with RaphaelJS

I'm trying to work out how to determine when an svg image has loaded in the browser. I'm using Raphael JS and I've tried:
var image = paper.image(path, 0,0,10,10);
image.node.addEventListener('load', function(){alert("test");});
and:
$('image').on('load')
all to no avail. I've also used "onload" and "onsvgload" none of which work.
Is there away to determine if an svg image has actually loaded?
I even tried loading the image using an Image() object and then calling paper.image() - but I get two calls to the image (instead of using the preloaded image);
ie:
var preload = new Image();
preload.src = imgPath;
preload.addEventListener('load', function () {
image.path = preload.src;
//Now load image in raphael - except this still forces the browser to make another call for the image
});
Any ideas?

Using the onLoad event handler works, with one additional line of code:
var image = paper.image(path, 0,0,10,10);
var image_node = image.node;
image_node.setAttribute('externalResourcesRequired','true');
image_node.addEventListener("load", function() {
console.log("image is loaded!");
})
You need to set the externalResourcesRequired attribute to true. You may read more about it here: http://www.w3.org/TR/SVG/struct.html#ExternalResourcesRequired

How to get the true image height using JQuery?

I want to load html , and then get the true image height.
$("#cover").html(stuff); //this has the image inside it
$(function(){
console.log($("#cover img").height()); //sometimes it's 0
});
For some reason, height is sometimes 0. Could it be because the image hasn't been fully loaded yet, and JQuery sees it as 0? If so, how do I overcome this? Is there a callback or something when the image is loaded?

You can use the .load() method of jQuery
$('#cover').html(stuff);
$('#cover img').load(function () {
console.log($(this).height());
};

Why do the console.log inside an anonymous function? Have you tried this?
$("#cover").html(stuff); //this has the image inside it
console.log($("#cover img").height());

//locate the image(s)
$("#cover img").each(function(){
//Build a new Image Object outside the DOM
//that way, CSS won't affect it
var img = new Image();
//add a callback when loaded
img.onload = function(){
//your width and height
//img.width
//img.height
}
//use the image src to load
//use attr() to resolve path issues across browsers
img.src = $(this).attr('src');
});

try to using load method method that we can take advantage of to make this work the way we want it too.
The problem we have right now is that, in the Webkit browsers, the jQuery code runs when the DOM is ready and the DOM is ready before the image has been loaded. So the code runs but since there’s no image to get a width of, we get 0 for the image’s width. We can use the load method to make the code wait until the window has loaded entirely before it runs.
$(window).load(function() {
console.log($("#cover img").height());
});

try using attr() to get the height:-
$("#yourElemengtID").attr('height')

Here is a piece of small code i used before hope this will help you
On my displayed image when mouse is in call this function
function MouseIn()
{
var src;
//to get original image size
var img =$(this);// displayed image
var theImage = new Image();// create a cache image
var imgsource =img.attr("src");// take the src of displayed image
theImage.src = imgsource;// give cached image the source of displayed image
var original_height = theImage.height// take height of image from the source
var original_width = theImage.width;//take width of image from the source
// to get the displayed image size
var Image_displaysize_width= img.width();
var Image_displaysize_height= img.height();
}

Don't you mean to do something like this?
jQuery("#myImg")[0].naturalHeight
better still don't use overhead of jQuery when possible.
document.getElementById('myImg').naturalHeight

Image width traces zero with onload when cached

I'm building a Javascript lightbox and I'm trying to adjust the size once the image has loaded. I'm using the code below, which works fine - it outputs the correct width once loaded.
My problem:
When I refresh, it will load the image instantly from the cache, and it seems to bypass the load. I get an instant zero for the width. Why does this happen?
My code:
var oImage = new Image();
oImage.src = 'http://mydomain.com/image.png';
container.html(oImage);
oImage.onload = function(){
alert(this.width);
}
** Update **
#Alex: This is the code I've tried with your plugin, I assume I'm probably doing something wrong. I'd be eager to get this working because your plugin looks quite good.
container.waitForImages(function() {
var cWidth = $(this).width();
alert("width: "+cWidth); // returns 0 - works first time but not cached
});
// Adding the image to the container for preload
container.html('<img src="mygraphic.png" />');

You need to do a few things...
Check the complete property of the img element.
Attach the load event before setting the src property.
Also, I found creating a new Image and assigning the src there is the best way to determine if the image has loaded or not.

You may want to switch the .html() and the .onload() calls.
If the image is loading from cache, I'm imagining that the .html() call completes before the script has had a chance to attach a function handler to the image's onload event. Therefore, effectively bypassing the load event itself (as the image has already loaded).
If it's still downloading the image (i.e. not cached), there will be more than enough time to call the .onload attach before the image completely finishes rendering.
While you're at it, you may want to do this the jQuery way, just so you're attaching events more similarly to DOM2 than DOM0.
var image = $('<img/>', {
src : 'http://mydomain.com/image.png'
}).load(function () {
alert(this.width);
})
// maybe clear container before if you want
.appendTo(container);
If we're going to have to set the src after the onload, we might as well do this instead:
var image = $('<img/>')
.load(function () {
alert(this.width);
})
.attr('src','http://mydomain.com/image.png')
.appendTo(container)
;
Hopefully that works cleanly.

This answer JavaScript: Know when an image is fully loaded suggests that you should set onload before setting 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'
]);
});