Cómo comprobar si una entrada de formulario de texto no vacía html

javascript comprobar si la entrada está vacía

<!-- check if any input field in "Form" is empty using JS -->

<script type="text/javascript">
  function validateForm() {
    var a = document.forms["Form"]["answer_a"].value;
    var b = document.forms["Form"]["answer_b"].value;
    if (!a || !b) {
      alert("Please Fill All Required Fields");
      return false;
    }
  }
</script>

<form method="post" name="Form" onsubmit="return validateForm()" action="">
  <input type="text" name="answer_a" value="">
  <input type="password" name="answer_b" value="password">
</form>