JavaScript alert recognizing as same line and showing alert

Question

In website, I made this. When I press enter, it recognize as new barcode in textarea. In JavaScript, I made inserted digits are no more than 6 and Shows alert if more than 6 digits. But in progress; If I hit enter, there will be new barcode (example, 111111 and 222222 (in next line)) but JavaScript alert is recognized as more than 6 and keeps showing alert. But If I only insert 1 barcode, it works well. My opinion is that JS didn't know for the second inserted barcodes. May I know How can I fix?

    $barcode_name = "Seal Number:";
            $barname = "placeholder=\"Enter 6 digits Serial Number.\"";

<br>
      <label class="control-label col-sm-4" for="seal_qty">Seal Quantity:</label>
      <div class="col-sm-4">
        <p class="form-control-static" style="margin-top: -6px;">
            <input type="number" class="form-control" id="seal_qty" name="seal_qty" min="1" placeholder="Enter Seal Quantity" value="<?php echo $seal_qty; ?>">
        </p>
      </div>
      <div class="col-sm-10"></div>

<br>
      <label class="control-label col-sm-4" for="barcodeno"><?php echo $barcode_name; ?></label>
      <div class="col-sm-4">
        <p class="form-control-static" style="margin-top: -6px;">
            <textarea class="form-control" rows="10" id="barcodeno" name="barcodeno" onkeydown="return KeyDown()" onkeyup="this.value=this.value.toUpperCase()" onkeypress="return isNumberKey(event)"<?php echo $barname; ?>></textarea>
            
        </p>
      </div>
      <br>

Below is Javascript.

var barcodeno = document.translot.barcodeno.value;
      if (barcodeno == ""){
          alert("Please Insert Serial Numbers.")
          return false;
      }
      
      else if (barcodeno.length != 6 ){
          alert("Barcode Numbers must be at lest 6 digits.")
          return false;
      }
      
  

  $('#filter').html(''); // to clear selection
  // lotid = $('#lotid').val().split('\n');
  var barcodeno = $('#barcodeno').val().trim();
  barcodeno = barcodeno.split('\n');
//checking duplicate barcodeno
    let barcodeno_array = []
    for(let i = 0;i < barcodeno.length; i++){
        if(barcodeno_array.indexOf(barcodeno[i]) == -1){
            barcodeno_array.push(barcodeno[i])
        }
    }
    
  var Barcode = barcodeno_array.length;
  //alert (Barcode+'||'+seal_qty);
  if (seal_qty != Barcode){
      alert ("Seal Quantity and Number of BarcodeID must be the same.");
      return false;
  }

Answer 1

var barcodenoStr = $('#barcodeno').val().trim();
let barcodes = barcodeStr.split("\n");
let allBarcodeValid = true;
let barcodeno_array = []
for(let i =0; i < barcodes.length; i++){
  let barcodeno = barcodes[i];
  if (barcodeno == "" || barcodeno.length != 6){
    allBarcodeValid = false;
    break;
  }
  //checking duplicate barcodeno
  if(barcodeno_array.indexOf(barcodes[i]) == -1){
    barcodeno_array.push(barcodes[i])
  }
}
if (!allBarcodeValid){
    alert("Entered barcodes are not valid");
    return false;
}
      
      
$('#filter').html(''); // to clear selection

  
//  seal_qty variable is missing

if (seal_qty != barcodeno_array.length;){
  alert ("Seal Quantity and Number of BarcodeID must be the same.");
  return false;
}