JavaScript Email Validation Using -Regular Expression

if(document.getElementById("<%=txtEmailid.ClientID %>").value=="")
                 {
                    alert("Please Enter Email-Id");
                    document.getElementById("<%=txtEmailid.ClientID %>").focus();
                    return false;
                 }
                 var emailPat = /^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$/;
                 var emailid=document.getElementById("<%=txtEmailid.ClientID %>").value;
                 var matchArray = emailid.match(emailPat);
                 if (matchArray == null)
                {
                    alert("Please Enter valid Email-Id.");
                    document.getElementById("<%=txtEmailid.ClientID %>").focus();
                    return false;
                }