How to clear textarea's default text

Often there may be requirements that a html form with a textarea containing a default text clears automatically when someone selects/clicks on the textarea.
This is achieved as below.

Time Picker using HTML and Java Script

Today while migrating the application, I was in need of having a textfield which takes time as an input. For this reason I needed a time picker, which will help the users to enter the time just by selecting something. I searched in web for this and found one from http://www.nogray.com/time_picker.php. This is very useful source for some most widely used javascripts like calendar, color picker, menubar etc.