JSFiddle - React, Tailwind, and code Playground

HTML

<select id="selectVendor">
 <option value="55" selected="selected">Company A</option>
 <option value="56">Company B</option>
 <option value="57">Company XYZCYK</option>
</select>
<br>
Option Count: <div id="count"></div>
Random: <div id="rand"></div>

JavaScript

var options = $("#selectVendor > option");

var random = Math.floor(options.length * (Math.random() % 1));

$("#selectVendor > option").attr('selected',false).eq(random).attr('selected',true);

$("#count").text(options.length);
$("#rand").text(random);