$(function () {

        var stack = new Undo.Stack(),

            EditCommand = Undo.Command.extend({

                constructor: function (textarea, oldValue, newValue) {

                    this.textarea = textarea;

                    this.oldValue = oldValue;

                    this.newValue = newValue;

                },

                execute: function () {},

                undo: function () {

                    this.textarea.html(this.oldValue);

                },

​

                redo: function () {

                    this.textarea.html(this.newValue);

                }

            });

        stack.changed = function () {

            stackUI();

        };

​

        var undo = $(".undo"),

            redo = $(".redo"),

            dirty = $(".dirty");

​

        function stackUI() {

            undo.attr("disabled", !stack.canUndo());

            redo.attr("disabled", !stack.canRedo());

            dirty.toggle(stack.dirty());

        }

        stackUI();

​

        $(document.body).delegate(".undo, .redo, .save", "click", function () {

            var what = $(this).attr("class");

            stack[what]();

            return false;

        });

​

        var text = $("#text"),

            startValue = text.html(),

            timer;

        $("#text").bind("keyup", function () {

            // a way too simple algorithm in place of single-character undo

            clearTimeout(timer);

            timer = setTimeout(function () {

                var newValue = text.html();

                // ignore meta key presses

                if (newValue != startValue) {

                    // this could try and make a diff instead of storing snapshots

                    stack.execute(new EditCommand(text, startValue, newValue));

                    startValue = newValue;

                }

            }, 50);

        });

​

        $(".bold").click(function () {

            document.execCommand("bold", false);

            var newValue = text.html();

            stack.execute(new EditCommand(text, startValue, newValue));

            startValue = newValue;

        });

​

        $(document).keydown(function (event) {

            if (!event.metaKey || event.keyCode != 90) {

                return;

            }

            event.preventDefault();

            if (event.shiftKey) {

                stack.canRedo() && stack.redo()

            } else {

                stack.canUndo() && stack.undo();

            }

        });

    });