JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-2.1.0.js"></script>
<select data-bind="options: venues, value:selectedVenue"></select>
<select data-bind="options: events, value:selectedEvent"></select>
<div data-bind="text: stuff"></div>

JavaScript

var vm = function() {
 var 
    venues = ko.observableArray([9,8,7,6,5,4,3,2,1]),
    events = ko.observableArray([]),
    selectedVenue = ko.observable(null),
    selectedEvent = ko.observable(null),
    stuff = ko.observable(),
    venueChange = ko.computed(function () {
        var venue = selectedVenue();
        if (venue) {
            alert(venue);
            var amt = Math.floor((Math.random()*10)+1);
            events([]);
            for(var i = 0; i < amt; i++){
             events.push(Math.floor((Math.random()*10)+1));
            }
            
            //Do stuff here such as load events/'your second list' 
            //events([1,2,3,4,5,6,7]);
        }
    }),
    eventChange = ko.computed(function () {
        var event = selectedEvent();
        if (event) {
            stuff('You Picked # ' + event);
            //Do stuff again
        }
    });
    
    return {
        venues:venues,
        events:events,
        selectedVenue: selectedVenue,
        selectedEvent: selectedEvent,
        stuff:stuff
    };
};
ko.applyBindings(new vm());