I need a help in this javascript output

JavaScript
1

I want to get user input from the html input colunm to the table below. if the input column are empty, I want the user to see error alert but if the columns were filled, I want the values shown in the table and user get an alert, “successful”. but now what i get is page not found response. Can someone point me to what is wrong.

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
    <meta name="viewport" content="width=width-device,initial-scale=1.0">
   <title> Expense tracker list </title>
</head>
<style>
body{
 background: #fff;
 
}
.tag {
   background:#ccc;
   width:100%;
   height:150px;
   font-size:20px;
   transform: uppercase;
   margin-top:30px;
   padding-top:30px;
   position: absolute;
   justify-space: in-between;

}
#item {
   width:19.35%;
   height:auto;
   background:pink;
   float:left;
   text-align:center;
   font-size:10px;
   border:1px solid black;
}

.item{
  width:19.35%;
   height:auto;
   background:pink;
   float:left;
   text-align:center;
   font-size:10px;
   border:1px solid black;
}

 .frame {
    width:90%;
    height:200px;
    background:grey;
    padding:10px;
    border-radius:3px;
    overflow-y:auto;
    float:left;
    position: relative;
    color:#231ccb;
  
}
</style>
<body>

<h1>Expense Tracker</h1>

<form action="iframe" method="GET">
 
   <div class="frame">
   <p><label> Item:<input type="text" name="itemName" placeholder="item" required> </label></p>
 <br>  <p><label> Quantity:<input type="text" name="itemQty" required> </label></p>
<br>   <p><label> Price :<input type="number" name="itemPrice" required> </label></p>
<!--<br>   <p><label> Amount: <input type="number" name="itemAmt" placeholder="#" required> </label></p>-->
<br>   <p><label> Date :<input type="Date" name="itemDate" required> </label></p>
   

</div>
<br>

   <button onclick="getValues()"> Add Item </button>
</form>
<!--Table Header-->
<div class="tag">
<div id="item">Item Name</div>
<div id="item">Quantity</div>
<div id="item">Price</div>
<div id="item">Amount</div>
<div id="item">Date</div>

<!--Display item variable-->
<div class="item">
<p id="itemName" ></p>
</div>

<div class="item">
<p id="itemQty" > </p>
</div>

<div class="item">
<p id="itemPrice" ></p>
</div>

<div class="item">
<p id="itemAmt" > </p>
</div>

<div class="item">
<p id="itemDate" ></p>
</div>




<br>
<br>
<br>

 <p id="tag"> Hello world</p>

</div>




<script>

      function getValues() {

let item = itemName;  
  if (item == null){
alert("Please you need to fill all fields  to continue");
else 
alert ("success")
}
//Data collection
         var itemName = document.getElementsByName("itemName")[0].value;
         var itemQty = document.getElementsByName("itemQty")[0].value;
         var itemPrice = document.getElementsByName("itemPrice")[0].value;
         var itemAmt = itemPrice * itemQty;
           
         var itemDate = document.getElementsByName("itemDate")[0].value;
         
         var total = "Your total amount of items bought is "  + " "+"#" + itemAmt;
     
//data display
         document.getElementById("tag").innerHTML= total;
         document.getElementById("itemName").innerHTML= (itemName);
         document.getElementById("itemQty").innerHTML= (itemQty);
         document.getElementById("itemPrice").innerHTML= (itemPrice);
         document.getElementById("itemAmt").innerHTML= (itemAmt);
         document.getElementById("itemDate").innerHTML= (itemDate);
    
//conditional statement for empty field

// if ( itemAmt === true){
            alert(total)
     //  }else{
           // alert("Please you need to fill all fields  to continue")
//}  
           
      }
   </script>
</body>
</html>