JSFiddle - React, Tailwind, and code Playground

HTML

<div data-bind="currency: value"></div>

JavaScript

ko.bindingHandlers.currency = {
    init: function(element, accessor) {
        var computed = ko.computed(function() {
            return ko.unwrap(accessor()) +" do custom formating";
        });
        ko.applyBindingsToNode(element, { text: computed });
    }
};

ko.applyBindings({ value: 1 });