get value onclick

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
  var x;
  if (confirm("Press a button!") == true) {
    x = "You pressed OK!";
  } else {
    x = "You pressed Cancel!";
  }
  document.getElementById("demo").innerHTML = x;
}
</script>