JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#" data-bind="click: child.method">foo</a>

JavaScript

function Child() {
    var self = this;
    self.method = function() {
         console.dir(self); // this should be 'p.child' <Child> since 
         //'method' called as a property of 'p.child'
         // but when you call it from KO it's actually 'p' <Parent>
    };
}

function Parent() {
    var self = this;
    self.child = new Child();
}
var p = new Parent();
ko.applyBindings(p);