lib/Ext/MessageBox.js
function(title, message, fn, scope) {
        return this.show({
            title       : title || null,
            message     : message || null,
            buttons     : Ext.MessageBox.YESNO,
            promptConfig: false,
            scope       : scope,
            fn: function() {
                if (fn) {
                    fn.apply(scope, arguments);
                }
            }
        });
    }
function(title, message, fn, scope) {
        return this.show({
            title       : title || null,
            message     : message || null,
            buttons     : Ext.MessageBox.YESNO,
            promptConfig: false,
            scope       : scope,
            fn: function() {
                if (fn) {
                    fn.apply(scope, arguments);
                }
            }
        });
    }
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} message The message box body text.
@param {Function} fn A callback function which is called when the dialog is dismissed by clicking on the configured buttons.
@param {String} fn.buttonId The `itemId` of the button pressed, one of: 'ok', 'yes', 'no', 'cancel'.
@param {String} fn.value Value of the input field if either `prompt` or `multiLine` option is `true`.
@param {Object} fn.opt The config object passed to show.
@param {Object} [scope] The scope (`this` reference) in which the callback is executed.

Defaults to: the browser window

@return {Ext.MessageBox} this