Problem with dynamic fields

[vitsid]

I have thi scenario :
5 dynamic fields
Dynamic field 1 dropdown menu values (1| 2) mandatory
Dynamic field 2 text field mandatory
Dynamic field 3 datetime mandatory
Dynamic filed 4 text field
Dynamic field 5 text field

I have this need, when Dynamic field 1 is equal 1 Dynamic filed 4 and 5 should be set to mandatory otherwise not.

I know that I have to solve it with javascript but where ?
I use otrs 5.0.7
Any help will beapreciate

Thanks in advance