<script src="joint.dia.command.js"></script>

var graph = new joint.dia.Graph;
var paper = new joint.dia.Paper({ el: $('#paper'), width: 500, height: 500, model: graph });

var commandManager = new joint.dia.CommandManager({ graph: graph });

$('#undo-button').click(function() { commandManager.undo(); });
$('#redo-button').click(function() { commandManager.redo(); });