var b="str is required"
function CheckForm(a,b)
{ 
if(a.value=="") 
{ 
alert(b); 
//document.a.focus(); 
return false; 
}
return true;
}

function checkmail()
{
    var email=document.form1.email.value;
    var pattern=/^([a-zA-Z0-9_-])+@([a-zA-Z0-9_-])+(\.[a-zA-Z0-9_-])+/;
    flag=pattern.test(email);
    if (flag)
    {return true;}
    else
        {
         alert('Please enter the correct mail address!');
        return false;
        }
}