function trim(s)
{
  return s.replace(/^\s+|\s+$/, '');
} 

function chk()
{

	var strEmail=document.Emailfrm.strEmail.value;
	var Fname=document.Emailfrm.strName.value;
	var Sname=document.Emailfrm.strLastName.value;
	Sname = trim(Sname);
	Fname = trim(Fname);
	var strEmail = trim(strEmail); 
	var pattern = /[^a-zA-Z]+/;
	var filter=/^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,3}(?:\.[a-z]{2})?)$/i;

 if(strEmail=="")
 {
	 document.getElementById("emailDiv").innerHTML="Please Enter a Valid Email id!";
	 document.getElementById("emailDiv").style.display="inline";
	 document.getElementById('strEmail').value = "";
	 document.getElementById('strEmail').focus();
	 return false;
 }else{
	var str=document.getElementById('strEmail').value;
	var aa=str.indexOf("@")
	var bb=str.indexOf(".")
	var cc=str.charAt(aa)
	
	if(aa==-1)
	{
		 document.getElementById("emailDiv").innerHTML="Please Enter a Valid Email id!";
		 document.getElementById("emailDiv").style.display="inline";
	 	 document.getElementById('strEmail').value = "";
	 	 document.getElementById('strEmail').focus();
		 return false;
	
	}else if(bb==-1){
		document.getElementById("emailDiv").innerHTML="Please Enter a Valid Email id!";
		document.getElementById("emailDiv").style.display="inline";
	 	document.getElementById('strEmail').value = "";
	        document.getElementById('strEmail').focus();
		return false;
	} 
 	
	if(filter.test(strEmail)== false)
	{
		 document.getElementById("emailDiv").innerHTML="Please Enter a Valid Email id!";
		 document.getElementById("emailDiv").style.display="inline";
	 	 document.getElementById('strEmail').value = "";
 		 document.getElementById('strEmail').focus();
		 return false;
	}

	if(aa!=-1 && bb!=-1 && filter.test(strEmail)== true)
	{
			document.getElementById('emailDiv').style.display="none";
	}
}
  if(pattern.test(Fname)){
        document.getElementById("emailDiv").innerHTML="Please Enter a valid First Name";
        document.getElementById("emailDiv").style.display="inline";
	document.getElementById('strName').value = "";
	document.getElementById('strName').focus();
	return false;	
        }
  if(pattern.test(Sname)){
        document.getElementById("emailDiv").innerHTML="Please Enter a valid  SurName";
        document.getElementById("emailDiv").style.display="inline";
	document.getElementById('strLastName').value = "";
	document.getElementById('strLastName').focus();
	return false;
        }
	return true;
}
<!-- OY - eblghws05dmz -->