MSCRM Can i set this base on current date and field By using Javascript???

Hi, I have 2 different field in my form (Timeline and Est. Close Date)

Example:
Today is 16/4/2013
In Timeline I select "This Year"
So, In Est. Close Date will auto populate date base on Current Date & Timeline, which is 31/12/2013

Just like :

Inside my Timeline I have (This Month, This Quarter, Next Quarter, This Year and next year)

Thank you!!