JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" data-bind="checked: myCheck" />Click me

JavaScript

var VM = function () {
    var self = this;
    self.myCheck = ko.observable(false);
    
    self.myCheck.subscribe(function(){
        alert(self.myCheck());
    });
}

ko.applyBindings(new VM());