JSFiddle - React, Tailwind, and code Playground

HTML

<select multiple>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>

JavaScript

var items = "1,2";
$.each(items.split(','), function(idx, val) {
    console.log(val);
    $("select option[value='"+val+"']").attr("selected", "selected");
});