Show right messages as soon as possible (#632)

* Flashed messaged should be flushed in every page

* Show error messages in AJAX style

* Introduce the decorator "api"

* Move toggleCheckbox() to the right place and trigger it in jQuery style

caravel/assets/javascripts/modules/utils.js

@@ -74,7 +74,30 @@ function showModal(options) {
   $(options.modalSelector).modal("show");
 }
 
+var showApiMessage = function (resp) {
+  var template = '<div class="alert"> ' +
+      '<button type="button" class="close" ' +
+      'data-dismiss="alert">×</button> </div>';
+
+  var severity = resp.severity || 'info';
+  $(template)
+      .addClass('alert-' + severity)
+      .append(resp.message)
+      .appendTo($('#alert-container'));
+};
+
+var toggleCheckbox = function (apiUrlPrefix, selector) {
+  var apiUrl = apiUrlPrefix + $(selector)[0].checked;
+  $.get(apiUrl).fail(function (xhr, textStatus, errorThrown) {
+    var resp = xhr.responseJSON;
+    if (resp && resp.message) {
+      showApiMessage(resp);
+    }
+  });
+};
+
 module.exports = {
   wrapSvgText: wrapSvgText,
-  showModal: showModal
+  showModal: showModal,
+  toggleCheckbox: toggleCheckbox
 };