height of textarea increases when value increased but does not reduce when value is decreased

Answer 1

The minimum scrollHeight of a textarea is always going to be the height. To get an accurate scrollHeight, set the height to 1 first.

h.height(1).height(h[0].scrollHeight);

http://jsfiddle.net/aarongloege/t2vAr/

Answer 2

If you do not want to code it by yourself, you can also use this script: https://github.com/brandonaaron/jquery-expandable It already contains a nice slide-effect ;-)