redo/undo manager

unre.js

var Manager = function (obj) {
    this.target = obj;
    this.history = [];
    this.step = -1;
    return this;
}

Manager.prototype.set = function (key, value) {
    var me = this,
        target = me.target;

    me.step = me.history.length;
    me.history.push({
        action: 'set',
        key: key,
        value: value,
        previousValue: target[key]
    });

    target[key] = value;
}

Manager.prototype.get = function (key) {
    return this.target[key];
}

Manager.prototype.del = function (key) {
    var me = this,
        target = me.target;

    me.step = me.history.length;
    me.history.push({
        action: 'del',
        key: key,
        value: undefined,
        previousValue: target[key]
    });

    delete target[key];
}

Manager.prototype.undo = function () {
    var me = this,
        step = me.step,
        target = me.target,
        history = me.history;

    if (step === -1) {
        throw new Error('nothing to undo.');
    }

    var operation = history[step];

    target[operation.key] = operation.previousValue;

    me.step = --step;
}

Manager.prototype.redo = function () {
    var me = this,
        step = me.step,
        target = me.target,
        history = me.history;

    if (step > history.length - 2) {
        throw new Error('nothing to redo.');
    }

    var operation = history[++step];

    if (operation.action === 'del') {
        delete target[operation.key];
    } else {
        target[operation.key] = operation.value;
    }

    me.step = step;
}

var undoRedo = function (obj) {
    return new Manager(obj);
}