Form validation, in javascript || get form data inside javascript

<form name="myForm" action="/action_page.php" onsubmit="return validateForm()" method="post">
   Name: <input type="text" name="fname">
   <input type="submit" value="Submit">
</form>

<script>
function validateForm() {
  var x = document.forms["myForm"]["fname"].value;
  if (x == "") {
    alert("Name must be filled out");
    return false;
  }
}
</script>