Validasi Form Input

<form action="index.php?menu=action" method="post" enctype="multipart/form-data"
  name="form1" onsubmit="return validate_form(this)";>
  Data: <input type=text name=data1>
  Type: <label><input type="radio" name="tipe" value="1">tipe1</label>
  <label><input type="radio" name="tipe" value="2">tipe2</label>
  <input type="submit" value="submit" name="update">
  </form>

validation script will be:

function validate_required(field,alerttxt) {
  with (field)
  {
     if (value==null||value=="")
        {alert(alerttxt);return false}
     else {return true}
  }
  }
  
  function validate_install(thisform) {
  with (thisform)
  {
    if (!document.form1.tipe[0].checked && !document.form1.tipe[1].checked) 
      {alert("Choose tipe1 or tipe2!");
       document.form1.tipe[0].focus();
       return false;}
    if (validate_required(data1,"Data must be filled out!")==false)
      {data1.focus();return false}
   }
   }

dapat pencerahan dari sini