Command Pattern in JavaScript

gistfile1.js

// see http://d.hatena.ne.jp/ashigeru/20090113/1231857274

function edit(start, end, chars, buf) {
  var undo = buf.val.slice(start, end);
  buf.val = buf.val.slice(0, start) + chars + buf.val.slice(end);
  return edit.bind(null, start, start + chars.length, undo);
}

function sequence(commands, buf) {
  var undos = [];
  commands.forEach(function (command) {
    undos.push(command(buf));
  });
  return sequence.bind(null, undos);
}

var buf = {val: 'Hello, world!'};
var com = sequence.bind(null, [edit.bind(null, 0, 5, 'こんにちは'), edit.bind(null, 12, 13, '???')]);
console.log(buf.val);
var undo = com(buf);
console.log(buf.val);
var redo = undo(buf);
console.log(buf.val);
redo(buf);
console.log(buf.val);

// Hello, world!
// こんにちは, world???
// Hello, world!
// こんにちは, world???