JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://knockoutjs.com/downloads/knockout-3.1.0.js"></script>
<select data-bind="options: availableCountries,
                   optionsText: function(item) {
                       return item.countryName + ' (pop: ' + item.countryPopulation + ')'
                   },
                   value: selectedCountry,
                   optionsCaption: 'Choose...'"></select>

JavaScript

var Country = function(name, population) {
        this.countryName = name;
        this.countryPopulation = population;
    };
var AppViewModel = function() {
    this.availableCountries = ko.observableArray([
            new Country("UK", 65000000),
            new Country("USA", 320000000),
            new Country("Sweden", 29000000),
         new Country("Sweden", 29000000)
        ]);
        this.selectedCountry = ko.observable();
};
   ko.applyBindings(new AppViewModel());