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() {
    console.log(this.value)
    // do something
  }
}

</script>