Passing Form Variables with Javascript

Hi I would like to know why this piece of code does not show an empty string alert like it should. I think I am not passing the text field variables correctly or something along those lines.
Help would be greatly appreciated

//Form PHP
 
<SCRIPT language="JavaScript">
 
<!--
 
 function checkForm() 
 {
      var err = "";
  
    err += checkLogin();//check for empty string
  
    if (err != "")
  	{
         alert(err);
       	 return false;
	 }
 
return true;
}
-->
 
</SCRIPT>
 
<Script language="javascript" src="validator.js"></Script>
</head>
/*
omit stuff
*/
 
<form id="Login" action="wel.php" name="frmLog"
onsubmit="return checkForm();">
 
/*
omit stuff
*/
<td><input type="text" name="logID" id="logID" class="form250"></td>
 
******************
 
//validator.js
// JavaScript Document
function checkLogin ()
{  
    var strng=document.frmLog.logId.value;//get log in txtfield
    var error=" ";
   
    if (strng == " ") 
    {
        error = "Your Login ID must not be empty.\n";
    }
     return error;
       
}

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