Validate user deatils Form-JavaScript

function validateData()
{

if(document.getElementById('txtUserNo').value=="")
alert("Please enter User No!");
else if(document.getElementById('txtUserName').value=="")
alert("Please enter User Name!");
else if(document.getElementById('txtPassword').value=="")
alert("Please enter Password!");
else if(document.getElementById('txtConPassword').value=="")
alert("Please re enter Password!");
else if(document.getElementById('cboTitle').value=="")
alert("Please select Title!");
else if(document.getElementById('txtFirstName').value=="")
alert("Please enter First Name!");
else if(document.getElementById('txtLastName').value=="")
alert("Please enter Last Name!");
else if(document.getElementById('cboDesignation').value=="")
alert("Please select Designation!");
else if(document.getElementById('txtNicNo').value=="")
alert("Please enter NIC No!");
else if(document.getElementById('cboGender').value=="")
alert("Please Select Gender!");
else if(document.getElementById('txtDateofbirth').value=="")
alert("Please Select Date of Birth!");
else if(document.getElementById('txtEmailAddress').value=="")
alert("Please enter Email Address!");
else
{
if(document.getElementById('txtPassword').value!=document.getElementById('txtConPassword').value)
alert("Passwords don't match!");
else
saveData();
}
}