function myFunc() {  console.log("entered");  document.write('Submitted Data');  var firstname = document.getElementById("fname").value;  var lastname = document.getElementById("lname").value;  document.writeln("Your full name is:" + firstname + lastname);}<form>  <label> Firstname </label>  <input type="text" name="firstname" id="fname" size="15" /> <br> <br>  <label> Lastname</label>  <input type="text" name="lastname" id="lname" size="15" /> <br> <br>  <label>       Gender :      </label><br>  <input type="radio" name="male" /> Male <br>  <input type="radio" name="female" /> Female  <br>  <br>  <input type="button" value="Submit" onclick="myFunc()" /></form>單擊提交后，它不會獲取名字并在控制臺中顯示錯誤值 null。有人可以幫忙嗎？整個代碼保存在一個 HTML 頁面中