Ascertain Needed Div Height To Fit Content?

I have a javascript that manipulates the DOM with content that will be
of variable heights. How can I ascertain how high my div needs to be in
order to show all content without scroll bars. Rather than just having
this happen automatically, I want the div to expand with a DHTML
animation. So, I need to know where to tell the script to stop
expanding. In pseudo-code:

function divAni(){
if(this.height > 0){
if(this.height > 0){
this.height = this.height - increment;
}
setTimeout(divAni,delay)
} else {
if(this.height < this.height.needed){
this.height = this.height + increment
}
setTimeout(divAni,delay);
}
}

I'm just not sure how to ascertain how tall the div needs to be for the
content to display.