title: Regex JavaScript - how to check if a string is all letters and then all numbers
body: <p>This would be ok: 'AAAAAAA1222222'
  This would be not ok: '1AAAAA'
  This would not be ok: 'AA1AA'</p>
  
  <p>Just looking for a way to check if a string is ALL letters and then ONLY letters afterward.</p>