Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
</head>
<body>
  <script>
    function addFromAtoB(a, b){
      var result = 0;

      for(var i = a; i <= b; i++){
        result += i;
      }
      return result;
    }
    document.write(addFromAtoB(1,100));
  </script>
</body>
</html>