Button disable unless both input fields have value

Question

I have a form with two input fields and a submit button on my page, I would like to have the feature that the \'submit\' button is disabled until there are

Answer 1

$(function(){
  $("#first_name, #second_name").bind("change keyup",
  function(){
     if($("#first_name").val() != "" && $("#second_name").val() != "")
        $(this).closest("form").find(":submit").removeAttr("disabled");
     else
        $(this).closest("form").find(":submit").attr("disabled","disabled"); 
  });
});