JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://knockoutjs.com/downloads/knockout-3.1.0.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/underscore.js/1.6.0/underscore-min.js"></script>
<select data-bind="options: displayedCountries,
                   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.displayedCountries = ko.computed( function () {
        return _.uniq( this.availableCountries(), false, ko.toJSON );
    }, this );
    this.selectedCountry = ko.observable();
};
ko.applyBindings(new AppViewModel());