document initially hidden javascript container

IPython/core/display.py

@@ -368,6 +368,11 b' class Javascript(DisplayObject):'
         in the frontend. If the data is a URL, the data will first be
         downloaded and then displayed. 
 
+        In the Notebook, the containing element will be available as `element`,
+        and jQuery will be available.  The output area starts hidden, so if
+        the js appends content to `element` that should be visible, then
+        it must call `container.show()` to unhide the area.
+
         Parameters
         ----------
         data : unicode, str or bytes

IPython/frontend/html/notebook/static/js/codecell.js

@@ -686,13 +686,14 b' var IPython = (function (IPython) {'
     };
 
 
-    CodeCell.prototype.append_javascript = function (js, e) {
+    CodeCell.prototype.append_javascript = function (js, container) {
         // We just eval the JS code, element appears in the local scope.
         var element = $("<div/>").addClass("box_flex1 output_subarea");
-        e.append(element);
+        container.append(element);
         // Div for js shouldn't be drawn, as it will add empty height to the area.
-        e.hide();
-
+        container.hide();
+        // If the Javascript appends content to `element` that should be drawn, then
+        // it must also call `container.show()`.
         eval(js);
     }