js file.

signInModal.js

function signInModal(){

  $( "#sign_in" ).dialog({
    modal: true,
    autoOpen: $("body").hasClass("show_login"),
    resizable: false,
    minWidth: 400
  }); 
  $("a.login, a#login_link").click(function(){
    $( "#sign_in" ).dialog("open");
    return false;
  });
  $('#sign_in form input[type="submit"]').unbind("click").click(function(){
    form = $("#sign_in form");
    form.find("img").show();
    form.find("input[type='submit']").attr("disabled","disabled");
    form.find("input[type='submit']").addClass("inactive");
    $.ajax({
      url: form.attr("action") + ".js",
      type: "post",
      dataType: "json",
      data: form.serialize(),
      complete: function(){
        form.find("img").hide();
        form.find("input[type='submit']").removeAttr("disabled");
        form.find("input[type='submit']").removeClass("inactive");
      },
      success: function(data, response){
        form.find(".sign_in_flash.notice").show();
        window.location = data.redirect;
      },
      error: function(){
        form.find(".sign_in_flash.error").show();
      },
      beforeSend: function(){
        form.find(".sign_in_flash").hide();
      }
    });
    return false;
  });
}