JavaScript CSV validation

Question

How to check for comma separated values in a text box and raise an alert if not found? And if there is it should be characters in it like A,B,C,D

  function validate()
   {
         //validate text box;
   }
  <input type="text" id="val" >A,B,C,D</input>
  <input type="button" id="save" onclick="validate()">  
 

Answer 1

/^[A-Za-z](?:,[A-Za-z])*$/.test(document.getElementById("val").value)