JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-2.2.0.js"></script>
<select data-bind="options: selectList, value: firstSelect"></select>
<select data-bind="options: selectList, value: secondSelect, minVal: firstSelect"></select>

JavaScript

ViewModel = function () {
    var self = this;
    self.firstSelect = ko.observable();
    self.secondSelect = ko.observable();
    self.selectList = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
};

ko.bindingHandlers.minVal = {
    update: function (element, valueAccessor) {
        var firstValue = ko.utils.unwrapObservable(valueAccessor());
        var firstNext = null;
        $(element).children().each(function () {
            var $this = $(this);
            if ($this.val() <= firstValue) {
                $this.attr('disabled', 'disabled');
            } else {
                if (firstNext == undefined) {
                    firstNext = $this.val();
                    if (firstNext >= $(element).val()) {
                        $(element).val(firstNext);
                        $(element).change();
                    }
                }
            }
        });
    }
};

var vm = new ViewModel();
ko.applyBindings(vm);