Which is better to do client side or server side validation?
In our situation we are using
JavaScript can be modified at runtime.
I suggest a pattern of creating a validation structure on the server, and sharing this with the client.
You'll need separate validation logic on both ends, ex:
"required"
attributes on inputs
client-side
field.length > 0
server-side.
But using the same validation specification will eliminate some redundancy (and mistakes) of mirroring validation on both ends.