Error Msg

HTML

<input type="text" name="fname" form="myForm">
<select id="select-sex" form="myForm" name="radios"> 
 <option id="opt-default" form="myForm" selected>Seleziona</option>
 <option id="sexuomo" name="radios" value="Male" form="myForm">Uomo</option>
 <option id="sexdonna" name="radios" value="Female" form="myForm">Donna</option>
</select>


<button onclick="validateForm()">Submit</button>
<form name="myForm" id="myForm" onsubmit="return validateForm()" method="post">
</form>

JavaScript

//Error Msg for input field
function validateForm() {
  let x = document.forms["myForm"]["fname"].value;
  if (x == "") {
    alert("Name must be filled out");
    return false;
  }
}