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How do I tell when an image has been fully loaded using javascript

Bigshowmg
Bigshowmg asked
on
Medium Priority
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Last Modified: 2012-05-07
Hi, I have a website with some pretty large background images. On the first page I want to preload the backgrounds for the other pages into the cache using javascript.
eg

<SCRIPT LANGUAGE = JAVASCRIPT>
   img1 = new Image();
   img2 = new Image();
   img1.src = "imageName1.gif";
   img2.src = "imageName2.gif"
</SCRIPT>
Is there a way in javascript of knowing when these images have all been downloaded?

Many thanks

Matt
Comment
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Yes there is. If you have an image with the name, say "myimage01" in your html code, you can access it's onLoad method as shown in the code:
<html>
<body>
<img name="myimage01" src="whatever.gif" width="100" height="50" onLoad="your script here">
</html>

Open in new window

Also, the image object also has an onLoad method so you could also use "img1.onload" in your code.

Author

Commented:
Thanks
IN RESPONSE TO YOUR FIRST POST
But the images that I'd be loading would not feature on the same page as the javascript. I just need to load them into the cache so other pages on the site don't take any time to download them. The first page will feature a loading image and I want this to disapear once the images have been downloaded.But the images that I'd be loading would not feature on the same page as the javascript. I just need to load them into the cache so other pages on the site don't take any time to download them. The first page will feature a loading image and I want this to disapear once the images have been downloaded.

AND THE SECOND
Could you give me an example of img1.onload? I assume it returns false until the image is loaded? Would I keep running a While loop until I get a TRUE or is there a less messy way?
Actually it's more like this:

img.onload = onLoadHandler;

Which is your function name.

Author

Commented:
So the function will automatically be called once the image has loaded? (sorry if I'm being obvious).
Also do you know if this works across all browsers?

Cheers

Matt
onLoad is an EVENT, therefore it executes when that "event" occurs. Somehow I do not think this is what you want.

Basically what you are trying to do is begin the downloading of the images as soon as someone enters the first page.

This you can accomplish by putting them in IMG tags and setting the display to none

<img src="mybackground.png" width="100px" height="100px" style="display: none">

The browser will load the image. If you are using PHP or ASP, you can point it to a folder and have it automatically generate that HTML.

Or you can create an array in Javascript with the image names in it, and write a function to generate their img code onload.
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Author

Commented:
Thats great, thanks for your help!!
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