I am trying to create a javascript function that will display a popup window with a given picture. The filename of the picture will be passed into the function. The code I have for the function so ...

The image probably isn't loaded by that time. I mean, it's probably a couple milliseconds, if that, between when you assign that src and when you ask for the width and height.

Here’s an interesting proof-of-concept that could be useful or hazardous depending on the situation in which you encounter it. [jklmnn] drew inspiration from the work of [Ange Albertini] who … ...