Browser-independent way to detect when image has been loaded

user_92587 0
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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.

dom javascript
9 Answers

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

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?

JasonBunting_17900

The only reliable way I've found is to do it all on the client-side like this...

var img = new Image();
img.onload = function() {
  alert('Done!');
}
img.src = '/images/myImage.jpg';
Josh_Stodola_544200

I think onload should work fine. Do you have to generate the markup for the images, or can you add them statically? If the latter, I'd suggest the following:

<img src="foo.png" class="classNeededToHideImage" onload="makeVisible(this)">

Alternatively, you can use window.onload to make all images visible at once - window.onload fires after all external ressources have finished loading.

If you want to add the images dynamically, you first have to wait for the DOM to be ready to be modified, ie use jQuery or implement your own DOMContentLoaded hack for browsers which don't support it natively.

Then, you create your image objects, assign onload listeners to make them visible and/or add them to the document.

Even better (but slightly more complicated) would be to create and start loading the images immediately when the script executes. On DOMContentLoaded, you'll have to check each image for complete to decide whether to add them immediately to the document or wait for the image's onload listener to fire.

Christoph_480150

Okay, I'll try to summarize the various partial answers here (including mine).

It would appear the answer is to use onload, which is "widely supported" though not officially required according to standards. Note that for IE in particular, you must set onLoad before setting the src attribute or it may not fire onload when loading an image from the cache. This seems like best practice in any case: set up your event handlers before you start firing events. Where onload is not supported, one should assume that the functionality simply isn't available.

user_925870

If im not mistaken in javascript an image tag has the events onload and onerror

here is an intersting bit of code i did to hide broken images

in a style tag

img.failed{
   display:none;
}

using the img onerror i had a piece of javascript that did this.className=failed and it would hide the image if it errored

however i may have misunderstood what your goal

user_926610

It would appear the answer is use onreadystatechange in IE, and onLoad in other browsers. If neither one is available, do something else. onLoad would be preferable, but IE doesn't fire it when loading an image from the cache, as noted in one of the answers below.

user_925870
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