Browser-independent way to detect when image has been loaded

Question

In IE, you can onreadystatechange. There's onload, but I read scary things. jQuery wraps up the DOM's load event quite nicely with "ready". It seems likely I am just ignorant of another nice library's implementation of image loading.

The context is that I am generating images dynamically (via server callbacks) that can take some time download. In my IE-only code I set the src of the img element, then when the onreadystatechange event fires with the "complete" status, I add it to the DOM so the user sees it.

I'd be happy with a "native" JavaScript solution, or a pointer to a library that does the work. There's so many libraries out there and I'm sure this is a case of me just not knowing about the right one. That said, we're already jQuery users, so I'm not eager to add a very large library just to get this functionality.

Answer 1

NOTE: I wrote this in 2010, the browsers in the wild were IE 8/9 beta, Firefox 3.x, and Chrome 4.x. Please use this for research purposes only, I doubt you could copy/paste this into a modern browser and have it work without issue.

WARNING: It is 2017 now I still get points on this now and then, please only use this for research purposes. I currently have no idea how to detect image loading status, but there are probably much more graceful ways of doing it than this... at least I seriously hope there are. I highly recommend NOT using my code in a production environment without more research.

WARNING Part Two Electric Boogaloo: It is 2019 now, most jQuery functionality is built into vanilla JS now. If you're still using it, it may be time to stop and consider heading over to MDN and reading up on some of the new and fun stuff vanilla JS has to offer.

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I'm a bit late to this party, maybe this answer will help someone else...

If you're using jQuery don't bother with the stock event handlers (onclick/onmouseover/etc), actually just stop using them altogether. Use the event methods they provided in their API.

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This will alert, before the image is appended to the body, because load event is triggered when the image is loaded into memory. It is doing exactly what you tell it to: create an image with the src of test.jpg, when test.jpg loads do an alert, then append it to the body.

var img = $('<img src="test.jpg" />'); img.load(function() {     alert('Image Loaded'); }); $('body').append(img); 

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This will alert, after the image is inserted into the body, again, doing what you told it to: create an image, set an event (no src set, so it hasn't loaded), append the image to the body (still no src), now set the src... now the image is loaded so the event is triggered.

var img = $('<img />'); img.load(function() {     alert('Image Loaded'); }); $('body').append(img); $img.attr('src','test.jpg'); 

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You can of course also add an error handler and merge a bunch of events using bind().

var img = $('<img />'); img.bind({     load: function() {         alert('Image loaded.');     },     error: function() {         alert('Error thrown, image didn\'t load, probably a 404.');     } }); $('body').append(img); img.attr('src','test.jpg'); 

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Per the request by @ChrisKempen ...

Here is a non-event driven way of determining if the images are broken after the DOM is loaded. This code is a derivative of code from an article by StereoChrome which uses naturalWidth, naturalHeight, and complete attributes to determine if the image exists.

$('img').each(function() {     if (this.naturalWidth === 0 || this.naturalHeight === 0 || this.complete === false) {         alert('broken image');     } }); 

Answer 2

According to the W3C spec, only the BODY and FRAMESET elements provide an "onload" event to attach to. Some browsers support it regardless, but just be aware that it is not required to implement the W3C spec.

Something that might be pertinent to this discussion, though not necessarily the answer you are in need of, is this discussion:

Image.onload event does not fire on Internet Explorer when image is in cache

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Something else that may be related to your needs, though it may not, is this info on supporting a synthesized "onload" event for any dynamically-loaded DOM element:

How can I determine if a dynamically-created DOM element has been added to the DOM?