How do you set a field as mandatory using client script? It feels like I'm missing something. SA says the property isMandatory is read only. But when I toggle that the stars appear next to the fields. But no validation on the field occurs on save. When I use nlapiSetFieldMandatory in the console it's the same thing. Do I have to implement the validation myself on save?

So far I know. isDisabled is supported in client code.

Yes the isMandatory adds the star in the UI, but it does not actually care when you save the record