==== HTML ====
<form id="frm1" name="frm1" method="post" onSubmit="return checkFrm()">
  <input type="text" id="txt1['fname']">
  <input type="text" id="txt1['lname']">
  <button type="submit">ส่งข้อมูล</button>
</form>

<h1 id="title">Javascript Testing</h1>


====== Java script =======

function checkFrm() {

    var check = false;
    var title = document.getElementById('title');
  title.innerHTML = document.getElementById("txt1['fname']").value;
  
  if((document.getElementById("txt1['fname']").value !== "") && 
     (document.getElementById("txt1['lname']").value !== ""))
  {
      check = true;
  }
  else
  {
       title.innerHTML = "check fails";
  }
    
  return check;
   
}

*** ตัวอย่างลองนำไปปรับใช้นะครับ

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