Get previous value of an observable in subscribe of same observable

Question

Is it possible in knockout to get the current value of an observable within a subscription to that observable, before it receives the new value?

Example:

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Answer 1

I have found that I can call peek() from a writable computed observable to get the before value.

Something like this (see http://jsfiddle.net/4MUWp):

var enclosedObservable = ko.observable();
this.myObservable = ko.computed({
    read: enclosedObservable,
    write: function (newValue) {
        var oldValue = enclosedObservable.peek();
        alert(oldValue);
        enclosedObservable(newValue);
    }
});