The source code

    /*!
     * Ext JS Library 3.4.0
     * Copyright(c) 2006-2011 Sencha Inc.
     * licensing@sencha.com
     * http://www.sencha.com/license
     */
    /**
     * @class Ext.MessageBox
     * Utility class for generating different styles of message boxes.  The alias Ext.Msg can also be used.
     * Note that the MessageBox is asynchronous.  Unlike a regular JavaScript alert (which will halt
     * browser execution), showing a MessageBox will not cause the code to stop.  For this reason, if you have code
     * that should only run after some user feedback from the MessageBox, you must use a callback function
     * (see the function parameter for {@link #show} for more details).
     * Example usage:
     *
    // Basic alert:
    Ext.Msg.alert('Status', 'Changes saved successfully.');

    // Prompt for user data and process the result using a callback:
    Ext.Msg.prompt('Name', 'Please enter your name:', function(btn, text){
        if (btn == 'ok'){
            // process text value and close...
        }
    });

    // Show a dialog using config options:
    Ext.Msg.show({
       title:'Save Changes?',
       msg: 'You are closing a tab that has unsaved changes. Would you like to save your changes?',
       buttons: Ext.Msg.YESNOCANCEL,
       fn: processResult,
       animEl: 'elId',
       icon: Ext.MessageBox.QUESTION
    });

     * @singleton
     */
    Ext.MessageBox = function(){
        var dlg, opt, mask, waitTimer,
            bodyEl, msgEl, textboxEl, textareaEl, progressBar, pp, iconEl, spacerEl,
            buttons, activeTextEl, bwidth, bufferIcon = '', iconCls = '',
            buttonNames = ['ok', 'yes', 'no', 'cancel'];

        // private
        var handleButton = function(button){
            buttons[button].blur();
            if(dlg.isVisible()){
                dlg.hide();
                handleHide();
                Ext.callback(opt.fn, opt.scope||window, [button, activeTextEl.dom.value, opt], 1);
            }
        };

        // private
        var handleHide = function(){
            if(opt && opt.cls){
                dlg.el.removeClass(opt.cls);
            }
            progressBar.reset();
        };

        // private
        var handleEsc = function(d, k, e){
            if(opt && opt.closable !== false){
                dlg.hide();
                handleHide();
            }
            if(e){
                e.stopEvent();
            }
        };

        // private
        var updateButtons = function(b){
            var width = 0,
                cfg;
            if(!b){
                Ext.each(buttonNames, function(name){
                    buttons[name].hide();
                });
                return width;
            }
            dlg.footer.dom.style.display = '';
            Ext.iterate(buttons, function(name, btn){
                cfg = b[name];
                if(cfg){
                    btn.show();
                    btn.setText(Ext.isString(cfg) ? cfg : Ext.MessageBox.buttonText[name]);
                    width += btn.getEl().getWidth() + 15;
                }else{
                    btn.hide();
                }
            });
            return width;
        };

        return {
            /**
             * Returns a reference to the underlying {@link Ext.Window} element
             * @return {Ext.Window} The window
             */
            getDialog : function(titleText){
               if(!dlg){
                    var btns = [];

                    buttons = {};
                    Ext.each(buttonNames, function(name){
                        btns.push(buttons[name] = new Ext.Button({
                            text: this.buttonText[name],
                            handler: handleButton.createCallback(name),
                            hideMode: 'offsets'
                        }));
                    }, this);
                    dlg = new Ext.Window({
                        autoCreate : true,
                        title:titleText,
                        resizable:false,
                        constrain:true,
                        constrainHeader:true,
                        minimizable : false,
                        maximizable : false,
                        stateful: false,
                        modal: true,
                        shim:true,
                        buttonAlign:"center",
                        width:400,
                        height:100,
                        minHeight: 80,
                        plain:true,
                        footer:true,
                        closable:true,
                        close : function(){
                            if(opt && opt.buttons && opt.buttons.no && !opt.buttons.cancel){
                                handleButton("no");
                            }else{
                                handleButton("cancel");
                            }
                        },
                        fbar: new Ext.Toolbar({
                            items: btns,
                            enableOverflow: false
                        })
                    });
                    dlg.render(document.body);
                    dlg.getEl().addClass('x-window-dlg');
                    mask = dlg.mask;
                    bodyEl = dlg.body.createChild({
                        html:'
    '
                    });
                    iconEl = Ext.get(bodyEl.dom.firstChild);
                    var contentEl = bodyEl.dom.childNodes[1];
                    msgEl = Ext.get(contentEl.firstChild);
                    textboxEl = Ext.get(contentEl.childNodes[2].firstChild);
                    textboxEl.enableDisplayMode();
                    textboxEl.addKeyListener([10,13], function(){
                        if(dlg.isVisible() && opt && opt.buttons){
                            if(opt.buttons.ok){
                                handleButton("ok");
                            }else if(opt.buttons.yes){
                                handleButton("yes");
                            }
                        }
                    });
                    textareaEl = Ext.get(contentEl.childNodes[2].childNodes[1]);
                    textareaEl.enableDisplayMode();
                    progressBar = new Ext.ProgressBar({
                        renderTo:bodyEl
                    });
                   bodyEl.createChild({cls:'x-clear'});
                }
                return dlg;
            },

            /**
             * Updates the message box body text
             * @param {String} text (optional) Replaces the message box element's innerHTML with the specified string (defaults to
             * the XHTML-compliant non-breaking space character '&#160;')
             * @return {Ext.MessageBox} this
             */
            updateText : function(text){
                if(!dlg.isVisible() && !opt.width){
                    dlg.setSize(this.maxWidth, 100); // resize first so content is never clipped from previous shows
                }
                // Append a space here for sizing. In IE, for some reason, it wraps text incorrectly without one in some cases
                msgEl.update(text ? text + ' ' : ' ');

                var iw = iconCls != '' ? (iconEl.getWidth() + iconEl.getMargins('lr')) : 0,
                    mw = msgEl.getWidth() + msgEl.getMargins('lr'),
                    fw = dlg.getFrameWidth('lr'),
                    bw = dlg.body.getFrameWidth('lr'),
                    w;

                w = Math.max(Math.min(opt.width || iw+mw+fw+bw, opt.maxWidth || this.maxWidth),
                        Math.max(opt.minWidth || this.minWidth, bwidth || 0));

                if(opt.prompt === true){
                    activeTextEl.setWidth(w-iw-fw-bw);
                }
                if(opt.progress === true || opt.wait === true){
                    progressBar.setSize(w-iw-fw-bw);
                }
                if(Ext.isIE && w == bwidth){
                    w += 4; //Add offset when the content width is smaller than the buttons.
                }
                msgEl.update(text || ' ');
                dlg.setSize(w, 'auto').center();
                return this;
            },

            /**
             * Updates a progress-style message box's text and progress bar. Only relevant on message boxes
             * initiated via {@link Ext.MessageBox#progress} or {@link Ext.MessageBox#wait},
             * or by calling {@link Ext.MessageBox#show} with progress: true.
             * @param {Number} value Any number between 0 and 1 (e.g., .5, defaults to 0)
             * @param {String} progressText The progress text to display inside the progress bar (defaults to '')
             * @param {String} msg The message box's body text is replaced with the specified string (defaults to undefined
             * so that any existing body text will not get overwritten by default unless a new value is passed in)
             * @return {Ext.MessageBox} this
             */
            updateProgress : function(value, progressText, msg){
                progressBar.updateProgress(value, progressText);
                if(msg){
                    this.updateText(msg);
                }
                return this;
            },

            /**
             * Returns true if the message box is currently displayed
             * @return {Boolean} True if the message box is visible, else false
             */
            isVisible : function(){
                return dlg && dlg.isVisible();
            },

            /**
             * Hides the message box if it is displayed
             * @return {Ext.MessageBox} this
             */
            hide : function(){
                var proxy = dlg ? dlg.activeGhost : null;
                if(this.isVisible() || proxy){
                    dlg.hide();
                    handleHide();
                    if (proxy){
                        // unghost is a private function, but i saw no better solution
                        // to fix the locking problem when dragging while it closes
                        dlg.unghost(false, false);
                    }
                }
                return this;
            },

            /**
             * Displays a new message box, or reinitializes an existing message box, based on the config options
             * passed in. All display functions (e.g. prompt, alert, etc.) on MessageBox call this function internally,
             * although those calls are basic shortcuts and do not support all of the config options allowed here.
             * @param {Object} config The following config options are supported:
             * animEl : String/ElementAn id or Element from which the message box should animate as it
             * opens and closes (defaults to undefined)
             * buttons : Object/BooleanA button config object (e.g., Ext.MessageBox.OKCANCEL or {ok:'Foo',
             * cancel:'Bar'}), or false to not show any buttons (defaults to false)
             * closable : BooleanFalse to hide the top-right close button (defaults to true). Note that
             * progress and wait dialogs will ignore this property and always hide the close button as they can only
             * be closed programmatically.
             * cls : StringA custom CSS class to apply to the message box's container element
             * defaultTextHeight : NumberThe default height in pixels of the message box's multiline textarea
             * if displayed (defaults to 75)
             * fn : FunctionA callback function which is called when the dialog is dismissed either
             * by clicking on the configured buttons, or on the dialog close button, or by pressing
             * the return button to enter input.
             * Progress and wait dialogs will ignore this option since they do not respond to user
             * actions and can only be closed programmatically, so any required function should be called
             * by the same code after it closes the dialog. Parameters passed:
             * buttonId : StringThe ID of the button pressed, one of:
             * ok
             * yes
             * no
             * cancel
             *
             * text : StringValue of the input field if either prompt
             * or multiline is true
             * opt : ObjectThe config object passed to show.
             *
             * scope : ObjectThe scope of the callback function
             * icon : StringA CSS class that provides a background image to be used as the body icon for the
             * dialog (e.g. Ext.MessageBox.WARNING or 'custom-class') (defaults to '')
             * iconCls : StringThe standard {@link Ext.Window#iconCls} to
             * add an optional header icon (defaults to '')
             * maxWidth : NumberThe maximum width in pixels of the message box (defaults to 600)
             * minWidth : NumberThe minimum width in pixels of the message box (defaults to 100)
             * modal : BooleanFalse to allow user interaction with the page while the message box is
             * displayed (defaults to true)
             * msg : StringA string that will replace the existing message box body text (defaults to the
             * XHTML-compliant non-breaking space character '&#160;')
             * multiline : Boolean
             * True to prompt the user to enter multi-line text (defaults to false)
             * progress : BooleanTrue to display a progress bar (defaults to false)
             * progressText : StringThe text to display inside the progress bar if progress = true (defaults to '')
             * prompt : BooleanTrue to prompt the user to enter single-line text (defaults to false)
             * proxyDrag : BooleanTrue to display a lightweight proxy while dragging (defaults to false)
             * title : StringThe title text
             * value : StringThe string value to set into the active textbox element if displayed
             * wait : BooleanTrue to display a progress bar (defaults to false)
             * waitConfig : ObjectA {@link Ext.ProgressBar#waitConfig} object (applies only if wait = true)
             * width : NumberThe width of the dialog in pixels
             *
             * Example usage:
             *
    Ext.Msg.show({
       title: 'Address',
       msg: 'Please enter your address:',
       width: 300,
       buttons: Ext.MessageBox.OKCANCEL,
       multiline: true,
       fn: saveAddress,
       animEl: 'addAddressBtn',
       icon: Ext.MessageBox.INFO
    });

             * @return {Ext.MessageBox} this
             */
            show : function(options){
                if(this.isVisible()){
                    this.hide();
                }
                opt = options;
                var d = this.getDialog(opt.title || " ");

                d.setTitle(opt.title || " ");
                var allowClose = (opt.closable !== false && opt.progress !== true && opt.wait !== true);
                d.tools.close.setDisplayed(allowClose);
                activeTextEl = textboxEl;
                opt.prompt = opt.prompt || (opt.multiline ? true : false);
                if(opt.prompt){
                    if(opt.multiline){
                        textboxEl.hide();
                        textareaEl.show();
                        textareaEl.setHeight(Ext.isNumber(opt.multiline) ? opt.multiline : this.defaultTextHeight);
                        activeTextEl = textareaEl;
                    }else{
                        textboxEl.show();
                        textareaEl.hide();
                    }
                }else{
                    textboxEl.hide();
                    textareaEl.hide();
                }
                activeTextEl.dom.value = opt.value || "";
                if(opt.prompt){
                    d.focusEl = activeTextEl;
                }else{
                    var bs = opt.buttons;
                    var db = null;
                    if(bs && bs.ok){
                        db = buttons["ok"];
                    }else if(bs && bs.yes){
                        db = buttons["yes"];
                    }
                    if (db){
                        d.focusEl = db;
                    }
                }
                if(Ext.isDefined(opt.iconCls)){
                  d.setIconClass(opt.iconCls);
                }
                this.setIcon(Ext.isDefined(opt.icon) ? opt.icon : bufferIcon);
                bwidth = updateButtons(opt.buttons);
                progressBar.setVisible(opt.progress === true || opt.wait === true);
                this.updateProgress(0, opt.progressText);
                this.updateText(opt.msg);
                if(opt.cls){
                    d.el.addClass(opt.cls);
                }
                d.proxyDrag = opt.proxyDrag === true;
                d.modal = opt.modal !== false;
                d.mask = opt.modal !== false ? mask : false;
                if(!d.isVisible()){
                    // force it to the end of the z-index stack so it gets a cursor in FF
                    document.body.appendChild(dlg.el.dom);
                    d.setAnimateTarget(opt.animEl);
                    //workaround for window internally enabling keymap in afterShow
                    d.on('show', function(){
                        if(allowClose === true){
                            d.keyMap.enable();
                        }else{
                            d.keyMap.disable();
                        }
                    }, this, {single:true});
                    d.show(opt.animEl);
                }
                if(opt.wait === true){
                    progressBar.wait(opt.waitConfig);
                }
                return this;
            },

            /**
             * Adds the specified icon to the dialog.  By default, the class 'ext-mb-icon' is applied for default
             * styling, and the class passed in is expected to supply the background image url. Pass in empty string ('')
             * to clear any existing icon. This method must be called before the MessageBox is shown.
             * The following built-in icon classes are supported, but you can also pass in a custom class name:
             *
    Ext.MessageBox.INFO
    Ext.MessageBox.WARNING
    Ext.MessageBox.QUESTION
    Ext.MessageBox.ERROR
             *
             * @param {String} icon A CSS classname specifying the icon's background image url, or empty string to clear the icon
             * @return {Ext.MessageBox} this
             */
            setIcon : function(icon){
                if(!dlg){
                    bufferIcon = icon;
                    return;
                }
                bufferIcon = undefined;
                if(icon && icon != ''){
                    iconEl.removeClass('x-hidden');
                    iconEl.replaceClass(iconCls, icon);
                    bodyEl.addClass('x-dlg-icon');
                    iconCls = icon;
                }else{
                    iconEl.replaceClass(iconCls, 'x-hidden');
                    bodyEl.removeClass('x-dlg-icon');
                    iconCls = '';
                }
                return this;
            },

            /**
             * Displays a message box with a progress bar.  This message box has no buttons and is not closeable by
             * the user.  You are responsible for updating the progress bar as needed via {@link Ext.MessageBox#updateProgress}
             * and closing the message box when the process is complete.
             * @param {String} title The title bar text
             * @param {String} msg The message box body text
             * @param {String} progressText (optional) The text to display inside the progress bar (defaults to '')
             * @return {Ext.MessageBox} this
             */
            progress : function(title, msg, progressText){
                this.show({
                    title : title,
                    msg : msg,
                    buttons: false,
                    progress:true,
                    closable:false,
                    minWidth: this.minProgressWidth,
                    progressText: progressText
                });
                return this;
            },

            /**
             * Displays a message box with an infinitely auto-updating progress bar.  This can be used to block user
             * interaction while waiting for a long-running process to complete that does not have defined intervals.
             * You are responsible for closing the message box when the process is complete.
             * @param {String} msg The message box body text
             * @param {String} title (optional) The title bar text
             * @param {Object} config (optional) A {@link Ext.ProgressBar#waitConfig} object
             * @return {Ext.MessageBox} this
             */
            wait : function(msg, title, config){
                this.show({
                    title : title,
                    msg : msg,
                    buttons: false,
                    closable:false,
                    wait:true,
                    modal:true,
                    minWidth: this.minProgressWidth,
                    waitConfig: config
                });
                return this;
            },

            /**
             * Displays a standard read-only message box with an OK button (comparable to the basic JavaScript alert prompt).
             * If a callback function is passed it will be called after the user clicks the button, and the
             * id of the button that was clicked will be passed as the only parameter to the callback
             * (could also be the top-right close button).
             * @param {String} title The title bar text
             * @param {String} msg The message box body text
             * @param {Function} fn (optional) The callback function invoked after the message box is closed
             * @param {Object} scope (optional) The scope (this reference) in which the callback is executed. Defaults to the browser wnidow.
             * @return {Ext.MessageBox} this
             */
            alert : function(title, msg, fn, scope){
                this.show({
                    title : title,
                    msg : msg,
                    buttons: this.OK,
                    fn: fn,
                    scope : scope,
                    minWidth: this.minWidth
                });
                return this;
            },

            /**
             * Displays a confirmation message box with Yes and No buttons (comparable to JavaScript's confirm).
             * If a callback function is passed it will be called after the user clicks either button,
             * and the id of the button that was clicked will be passed as the only parameter to the callback
             * (could also be the top-right close button).
             * @param {String} title The title bar text
             * @param {String} msg The message box body text
             * @param {Function} fn (optional) The callback function invoked after the message box is closed
             * @param {Object} scope (optional) The scope (this reference) in which the callback is executed. Defaults to the browser wnidow.
             * @return {Ext.MessageBox} this
             */
            confirm : function(title, msg, fn, scope){
                this.show({
                    title : title,
                    msg : msg,
                    buttons: this.YESNO,
                    fn: fn,
                    scope : scope,
                    icon: this.QUESTION,
                    minWidth: this.minWidth
                });
                return this;
            },

            /**
             * Displays a message box with OK and Cancel buttons prompting the user to enter some text (comparable to JavaScript's prompt).
             * The prompt can be a single-line or multi-line textbox.  If a callback function is passed it will be called after the user
             * clicks either button, and the id of the button that was clicked (could also be the top-right
             * close button) and the text that was entered will be passed as the two parameters to the callback.
             * @param {String} title The title bar text
             * @param {String} msg The message box body text
             * @param {Function} fn (optional) The callback function invoked after the message box is closed
             * @param {Object} scope (optional) The scope (this reference) in which the callback is executed. Defaults to the browser wnidow.
             * @param {Boolean/Number} multiline (optional) True to create a multiline textbox using the defaultTextHeight
             * property, or the height in pixels to create the textbox (defaults to false / single-line)
             * @param {String} value (optional) Default value of the text input element (defaults to '')
             * @return {Ext.MessageBox} this
             */
            prompt : function(title, msg, fn, scope, multiline, value){
                this.show({
                    title : title,
                    msg : msg,
                    buttons: this.OKCANCEL,
                    fn: fn,
                    minWidth: this.minPromptWidth,
                    scope : scope,
                    prompt:true,
                    multiline: multiline,
                    value: value
                });
                return this;
            },

            /**
             * Button config that displays a single OK button
             * @type Object
             */
            OK : {ok:true},
            /**
             * Button config that displays a single Cancel button
             * @type Object
             */
            CANCEL : {cancel:true},
            /**
             * Button config that displays OK and Cancel buttons
             * @type Object
             */
            OKCANCEL : {ok:true, cancel:true},
            /**
             * Button config that displays Yes and No buttons
             * @type Object
             */
            YESNO : {yes:true, no:true},
            /**
             * Button config that displays Yes, No and Cancel buttons
             * @type Object
             */
            YESNOCANCEL : {yes:true, no:true, cancel:true},
            /**
             * The CSS class that provides the INFO icon image
             * @type String
             */
            INFO : 'ext-mb-info',
            /**
             * The CSS class that provides the WARNING icon image
             * @type String
             */
            WARNING : 'ext-mb-warning',
            /**
             * The CSS class that provides the QUESTION icon image
             * @type String
             */
            QUESTION : 'ext-mb-question',
            /**
             * The CSS class that provides the ERROR icon image
             * @type String
             */
            ERROR : 'ext-mb-error',

            /**
             * The default height in pixels of the message box's multiline textarea if displayed (defaults to 75)
             * @type Number
             */
            defaultTextHeight : 75,
            /**
             * The maximum width in pixels of the message box (defaults to 600)
             * @type Number
             */
            maxWidth : 600,
            /**
             * The minimum width in pixels of the message box (defaults to 100)
             * @type Number
             */
            minWidth : 100,
            /**
             * The minimum width in pixels of the message box if it is a progress-style dialog.  This is useful
             * for setting a different minimum width than text-only dialogs may need (defaults to 250).
             * @type Number
             */
            minProgressWidth : 250,
            /**
             * The minimum width in pixels of the message box if it is a prompt dialog.  This is useful
             * for setting a different minimum width than text-only dialogs may need (defaults to 250).
             * @type Number
             */
            minPromptWidth: 250,
            /**
             * An object containing the default button text strings that can be overriden for localized language support.
             * Supported properties are: ok, cancel, yes and no.  Generally you should include a locale-specific
             * resource file for handling language support across the framework.
             * Customize the default text like so: Ext.MessageBox.buttonText.yes = "oui"; //french
             * @type Object
             */
            buttonText : {
                ok : "OK",
                cancel : "Cancel",
                yes : "Yes",
                no : "No"
            }
        };
    }();

    /**
     * Shorthand for {@link Ext.MessageBox}
     */
    Ext.Msg = Ext.MessageBox;