How to resize iframe when content's getting smaller?

Question

I have been googling for a while, and found some similar topics on iframe resizing,
and actually I learned a lot from those, such as
1. Resize iframe to content with Jquery
2. Adding Dynamic Contents to IFrames
thanks for those people who contributed to answer those questions.
but I still got some questions which is not resolved,
so do you guys have any idea how to resize iframe when content's getting smaller?
In my case, I was trying to get content height either using
document.documentElement.scrollHeight or document.body.scrollHeight, but it won't work.
I guess it's hard to get the correct content height from outside, should we need a height
parameter to be passed to the resize function?

Answer 1

You need to use document.body.offsetHeight.

Answer 2

Whit testing on different sites and browsers, I finally got the best results for the height whit this code:

var height = document.documentElement.offsetHeight;
if(document.all) height = Number(document.body.clientHeight) + Number(document.body.bottomMargin) + Number(document.body.topMargin); // IE v <= 10