Untitled

<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
  </head>
  <body>
    <div>
      <form class="form1" action="submit">
        <input type="radio" name="radio1" class="radio" value="a" />a
        <input type="radio" name="radio1" class="radio" value="b" />b
        <input type="radio" name="radio1" class="radio" value="c" />c
      </form>
    </div>
  </body>
</html>

<script>
  var radio = document.querySelectorAll('.radio')
  for (var i = 0; i < radio.length; i++) {
    radio[i].onclick = function() {
      if (this.value === 'a') {
        // do something when a
      } else if (this.value === 'b') {
        // do something when b
      } else if (this.value === 'c') {
        // do something when c
      } else {
        // error handling
      }
      // switch(this.value) {
      //   case "a":
      //     console.log("here is for a");
      //     break;
      //   case "b":
      //     console.log("b block");
      //     break;
      //   case "c":
      //     console.log("c block!");
      //     break;
      //   default:
      //     console.log("if error?")
      // }
    }
  }
</script>