How to Get height of hidden element?

What is the role of obtaining the height of a hidden element?
Scenario:
A dialog plug-in
Dialog. Show (URL)
1. Display Loading
2. Use IFRAME to load the URL
3. IFRAME is loaded and the height of IFRAME is automatically adjusted.
4. Display dialog and hide Loading

Step 2: automatically adjust the IFRAME height. We can use $ IFRAME. Contents (). Find ("body"). Height () to obtain the height of the content in IFRAME.
However, since the dialog is not displayed, the obtained height is always 0, so we cannot automatically adjust the IFRAME height.

Solution:
Use visibility: hidden; display: block; replace display: none when hiding. In this way, we can get the height.
Use visibility: block when displaying;