Validating on Client side is better
because if you are using server side validation then entire data will be submitted to server and then the validation will be performed(Which is waste)
If you check at database side then also you need to establish connection to database and then you will come to know that format is wrong.
and Client side validations restrict the submission of data until you enter correct format.
So go with Client side validations.
[EDIT]-------
Yes there are chances that a user can disable javascript.
So perform both ways as said by Uma sankar to get better Validation of your fields.
Go through this link so that you will get some info regarding check constraint
http://docs.oracle.com/cd/B19306_01/appdev.102/b14251/adfns_constraints.htm#i1006547[
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