diff --git a/IPython/html/static/notebook/js/cell.js b/IPython/html/static/notebook/js/cell.js
index ec3daa0..4a87ba6 100644
--- a/IPython/html/static/notebook/js/cell.js
+++ b/IPython/html/static/notebook/js/cell.js
@@ -39,18 +39,28 @@ 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 = {
@@ -295,6 +305,7 @@ var IPython = (function (IPython) {
             this.code_mirror.setOption('mode', mode);
             return;
         }
+        var current_mode = this.code_mirror.getOption('mode', mode);
         var first_line = this.code_mirror.getLine(0);
         // loop on every pairs
         for( var mode in modes) {
@@ -303,6 +314,9 @@ var IPython = (function (IPython) {
             for(var reg in regs ) {
                 // here we handle non magic_modes
                 if(first_line.match(regs[reg]) != null) {
+                    if(current_mode == mode){
+                        return;
+                    }
                     if (mode.search('magic_') != 0) {
                         this.code_mirror.setOption('mode', mode);
                         CodeMirror.autoLoadMode(this.code_mirror, mode);
@@ -312,6 +326,9 @@ var IPython = (function (IPython) {
                     var close = modes[mode]['close']|| "%%end";
                     var mmode = mode;
                     mode = mmode.substr(6);
+                    if(current_mode == mode){
+                        return;
+                    }
                     CodeMirror.autoLoadMode(this.code_mirror, mode);
                     // create on the fly a mode that swhitch between
                     // plain/text and smth else otherwise `%%` is
@@ -339,6 +356,9 @@ var IPython = (function (IPython) {
         } catch(e) {
             default_mode = 'text/plain';
         }
+        if( current_mode === default_mode){
+            return
+        }
         this.code_mirror.setOption('mode', default_mode);
     };
 
diff --git a/IPython/html/static/notebook/js/codecell.js b/IPython/html/static/notebook/js/codecell.js
index ea00928..9b32496 100644
--- a/IPython/html/static/notebook/js/codecell.js
+++ b/IPython/html/static/notebook/js/codecell.js
@@ -62,11 +62,17 @@ 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 @@ 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);
     };
 
     /**
@@ -202,8 +202,10 @@ var IPython = (function (IPython) {
                 return true;
         } else if (event.keyCode === key.TAB && event.type == 'keydown') {
             // Tab completion.
-            //Do not trim here because of tooltip
-            if (editor.somethingSelected()) { return false; }
+            IPython.tooltip.remove_and_cancel_tooltip();
+            if (editor.somethingSelected()) {
+                return false;
+            }
             var pre_cursor = editor.getRange({line:cur.line,ch:0},cur);
             if (pre_cursor.trim() === "") {
                 // Don't autocomplete if the part of the line before the cursor
@@ -443,7 +445,8 @@ var IPython = (function (IPython) {
         var data = IPython.Cell.prototype.toJSON.apply(this);
         data.input = this.get_text();
         data.cell_type = 'code';
-        if (this.input_prompt_number) {
+        // is finite protect against undefined and '*' value
+        if (isFinite(this.input_prompt_number)) {
             data.prompt_number = this.input_prompt_number;
         }
         var outputs = this.output_area.toJSON();
diff --git a/IPython/html/static/notebook/js/notebook.js b/IPython/html/static/notebook/js/notebook.js
index ac10cef..67a27a7 100644
--- a/IPython/html/static/notebook/js/notebook.js
+++ b/IPython/html/static/notebook/js/notebook.js
@@ -1588,7 +1588,7 @@ var IPython = (function (IPython) {
                     cell_data.cell_type = 'raw';
                 }
 
-                new_cell = this.insert_cell_below(cell_data.cell_type);
+                new_cell = this.insert_cell_at_bottom(cell_data.cell_type);
                 new_cell.fromJSON(cell_data);
             };
         };
diff --git a/IPython/html/static/notebook/js/outputarea.js b/IPython/html/static/notebook/js/outputarea.js
index 12f219f..912e2ba 100644
--- a/IPython/html/static/notebook/js/outputarea.js
+++ b/IPython/html/static/notebook/js/outputarea.js
@@ -576,12 +576,13 @@ var IPython = (function (IPython) {
 
     OutputArea.prototype.append_png = function (png, md, element) {
         var toinsert = this.create_output_subarea(md, "output_png");
-        var img = $("<img/>").attr('src','data:image/png;base64,'+png);
+        var img = $("<img/>");
+        img[0].setAttribute('src','data:image/png;base64,'+png);
         if (md['height']) {
-            img.attr('height', md['height']);
+            img[0].setAttribute('height', md['height']);
         }
         if (md['width']) {
-            img.attr('width', md['width']);
+            img[0].setAttribute('width', md['width']);
         }
         this._dblclick_to_reset_size(img);
         toinsert.append(img);