A JavaScript question

So programming questions are now to be filed here in the software forum?

I have a JavaScript, and in there I need to know the dimensions of an image. Here is what I do

Code:

    testImage = new Image(); 
    testImage.src = 'http://....jpg';
    setTimeout(function()
        {checkImage(testImage);},
        256);

In the checkImage function I can obtain testImage.eight and testImage.width.

If I test the height or width immediately after I assign the image URL, both are 0. After that delay of a ¼ sec, both values are there.

My questions:

1. what makes the properties appear after a short delay?
2. is there a way to force the image to be loaded and properties set, inline (without calling setTimeout)?

 

Found something much more clever than an arbitrary delay: onload

Code:

testImage = new Image(); 
    testImage.src = 'http://....jpg';
    testImage.onload = function()
        {checkImage(testImage);};

It's not "inline", but at the end it does a better job than using setTimeout.

But, any comments welcome! :cool