javascript determine if my variable is null

javascript determine if my variable is null

$(function(){
//To send data from input text
$('#add').click(function(){
var name = $('#name').val();
var gender = $('#gender').val();
var age = $('#age').val();
var address = $('#address').val();
var illness = $('#illness').val();
var selectunit = $('#selectunit').val();
if (typeof name !== null) { my codes here... }
else{
alert('Some fields are missing!');
}
return false;
});
});
i want to trap my variables (name,age,address,illness) not to be null
before doing the codes please help thanks