some optimisation and code cleaning

optimisation are not obvious, but order and time of attribute creation
in javascript have impact for VMs apparently (Google IO talk on V8)

IPython/html/static/notebook/js/cell.js

@@ -39,18 +39,28 b' var IPython = (function (IPython) {'
         this.placeholder = options.placeholder || '';
         this.read_only = options.cm_config.readOnly;
         this.selected = false;
-        this.element = null;
         this.metadata = {};
         // load this from metadata later ?
         this.user_highlight = 'auto';
         this.cm_config = options.cm_config;
+        this.cell_id = utils.uuid();
+        this._options = options;
+
+        // For JS VM engines optimisation, attributes should be all set (even
+        // to null) in the constructor, and if possible, if different subclass
+        // have new attributes with same name, they should be created in the
+        // same order. Easiest is to create and set to null in parent class.
+
+        this.element = null;
+        this.cell_type = null;
+        this.code_mirror = null;
+
+
         this.create_element();
         if (this.element !== null) {
             this.element.data("cell", this);
             this.bind_events();
         }
-        this.cell_id = utils.uuid();
-        this._options = options;
     };
 
     Cell.options_default = {
@@ -309,7 +319,6 b' var IPython = (function (IPython) {'
                     }
                     if (mode.search('magic_') != 0) {
                         this.code_mirror.setOption('mode', mode);
-                        console.log('from',current_mode,'to',mode)
                         CodeMirror.autoLoadMode(this.code_mirror, mode);
                         return;
                     }
@@ -336,7 +345,6 b' var IPython = (function (IPython) {'
                         );
                     });
                     this.code_mirror.setOption('mode', mmode);
-                    console.log('from',current_mode,'to', mmode)
                     return;
                 }
             }
@@ -352,7 +360,6 b' var IPython = (function (IPython) {'
             return
         }
         this.code_mirror.setOption('mode', default_mode);
-        console.log('from',current_mode,'to', default_mode)
     };
 
     IPython.Cell = Cell;

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

@@ -62,11 +62,17 b' var IPython = (function (IPython) {'
      */
     var CodeCell = function (kernel, options) {
         this.kernel = kernel || null;
-        this.code_mirror = null;
-        this.input_prompt_number = null;
         this.collapsed = false;
         this.cell_type = "code";
 
+        // create all attributed in constructor function
+        // even if null for V8 VM optimisation
+        this.input_prompt_number = null;
+        this.celltoolbar = null;
+        this.output_area = null;
+        this.last_msg_id = null;
+        this.completer = null;
+
 
         var cm_overwrite_options  = {
             onKeyEvent: $.proxy(this.handle_codemirror_keyevent,this)
@@ -129,13 +135,7 b' var IPython = (function (IPython) {'
         cell.append(input).append(output);
         this.element = cell;
         this.output_area = new IPython.OutputArea(output, true);
-
-        // construct a completer only if class exist
-        // otherwise no print view
-        if (IPython.Completer !== undefined)
-        {
-            this.completer = new IPython.Completer(this);
-        }
+        this.completer = new IPython.Completer(this);
     };
 
     /**