JSFiddle - React, Tailwind, and code Playground

HTML

<input data-bind="value: data">

JavaScript

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

ko.applyBindings({data: myObservable});