import React from 'react'
import useForm from 'react-hook-form'

function App() {
  const { register, handleSubmit, errors } = useForm() // initialise the hook
  const onSubmit = (data) => { console.log(data) } // callback when validation pass
    
  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input name="firstname" ref={register} /> {/* register an input */}
      
      <input name="lastname" ref={register({ required: true })} /> {/* apply required validation */}
      {errors.lastname && 'Last name is required.'}
      
      <input name="age" ref={register({ pattern: /\d+/ })} /> {/* apply pattern validation */}
      {errors.age && 'Please enter number for age.'}
      
      <input type="submit" />
    </form>
  )
}