how to expand a text area when click on

Question

Im working on a small project which has a textarea and i need help in making the text area expand on mouse click like that of twitter and facebook. the textarea should look lik

Answer 1

var ta = document.getElementById('ta');
ta.onclick = function(){
    this.style.height = "400px";
}  

A quick fiddle: http://jsfiddle.net/n6sgT/