UI Page How to make mandatory text area field

Hi @ANKUR BAWISKAR

How to make mandatory text area field  in UI page?
Let me know how to client script in ui page 
I wanna use this UI pages on change request table  , Some one changes Planned start& end date to past date they mentioned additional information makes mandatory , Below screenshot when i on click uiaction button on change request table

whatever reflects UI page output should reflect on my Change request table

Please help me on this @Ankur Bawiskar 

Regards ,

Suresh