HTML5 required attribute one of two fields

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form method="post">
  Telephone:
  <input type="tel" name="telephone" value="" required>
  <br>Mobile:
  <input type="tel" name="mobile" value="" required>
  <br>
  <input type="submit" value="Submit">
</form>

<script>

jQuery(function ($) {

    var $inputs = $('input[name=telephone],input[name=mobile]');
    $inputs.on('input', function () {
        // Set the required property of the other input to false if this input is not empty.
        $inputs.not(this).prop('required', !$(this).val().length);
    });

});

</script>