JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://rawgit.com/bowerjs/knockout/master/knockout.js"></script>

<ul data-bind="foreach: names">
    <li data-bind="text: $data.myFunction()"></li>
</ul>

JavaScript

String.prototype.myFunction = function(){
	return this + '--';
}

function demoViewModel() {
	self.names = ['a', 'b', 'c'];
    
    return self;
}

var mm = new demoViewModel();

ko.applyBindings(mm);