Represents the command used to perform an undo of the most recent edit or action.
* The command has a boolean field canUndo that indicates whether the command supports undo and redo operations, and an execute method that performs an execute or undo operation.
* The arguments of the execute method are as follows.
context {GC.Spread.Sheets.Workbook} The context of the operation.
options {Object} The options of the operation.
* options.sheetName {string} The sheet name.
isUndo {boolean} true if this is an undo operation; otherwise, false.

var value; // Type: undo
value = GC.Spread.Sheets.Commands.undo;

var undo : undo;

$("#button1").click(function () {
                if(spread.undoManager().canUndo()){
                    spread.undoManager().undo();
                }
            });

            $("#button2").click(function () {
                if(spread.undoManager().canRedo()){
                    spread.undoManager().redo();
                }
            });