JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" data-bind="value: someText, customBinding: someText">

JavaScript

ko.bindingHandlers.customBinding = {
	update: function(element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
        var value = ko.utils.unwrapObservable(valueAccessor());
        console.log( JSON.stringify(value) );
    }
}

ko.applyBindings({
    someText: ko.observable("inital value")
});