typescript 1

t.ts

type Item = {
  Foo: string,
  Bar: string,
  // ...
}

function validate(item: Item): string[] {
   const required = ['Foo', ... ]
   return required.reduce((errors: string[], field) => {
       if (item[field] == null) errors.push(`${field} is required`)
       return errors
   }, [])
}