JSFiddle - React, Tailwind, and code Playground
HTML
<select name="countries" id="countries" MULTIPLE size="8">
<option value="UK">UK</option>
<option value="US">US</option>
<option value="Canada">Canada</option>
<option value="France">France</option>
<option value="India">India</option>
<option value="China">China</option>
</select>
JavaScript
$('#select').click(function() {
$('#countries option').prop('selected', true);
});