A "multi-level undo" extender for Knockout observables.

knockout-undoBuffer.js

ko.extenders.undoBuffer = function (target, maxUndo) {
    var undoBuffer = ko.observableArray([]), undoing;

    target.canUndo = ko.computed(function () {
        return undoBuffer().length > 0;
    });
    target.undo = function () {
        if (!target.canUndo()) return;
        undoing = true;
        target(undoBuffer.pop());
        undoing = false;
    };

    target.subscribe(function (oldValue) {
        if (undoing) return;
        if (undoBuffer().length === maxUndo) undoBuffer.shift();
        undoBuffer.push(oldValue);
    }, null, "beforeChange");

    return target;
};

// usage:
this.fooValue = ko.observable().extend({undoBuffer: 10});

// bindings:
// <input data-bind="value: fooValue">
// <button click: fooValue.undo, enable: fooValue.canUndo">Undo</button>