JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <select multiple='multiple' data-bind="options: myList"></select>
</body>

JavaScript

var vm = function() {
    var self = this;
    
    self.myList = ko.observableArray();
    
    self.myList.push('Option 1');
    self.myList.push('Option 2');
    self.myList.push('Option 3');
}

if (window.addEventListener) {
    window.addEventListener('load', function() {
        var viewModel = vm();
        ko.applyBindings(viewModel);
    }, false); // NB **not** 'onload'
} else if (window.attachEvent) {
    window.attachEvent('onload', function () {
        var viewModel = vm();
        ko.applyBindings(viewModel);
    });
}