JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://knockoutjs.com/downloads/knockout-2.2.0.debug.js"></script>
<input data-bind="value: firstName, valueUpdate:'afterkeydown'" type="text" />

<button data-bind="myhandler: firstName" >Click</button>

JavaScript

ko.bindingHandlers.myhandler =
        {
            update: function (element, valueAccessor) {
                
                $(element).css("background", "red");
                console.log('update');

            }
        
        }


    var vm = function () {
        this.firstName = ko.observable('bert');

    }

    ko.applyBindings(new vm());