JSFiddle - React, Tailwind, and code Playground

HTML

<select id="dropdown">
	<option>...</option>
	<option>foo</option>
	<option>bar</option>
</select>

<input type="checkbox" id="checkbox" />
<input type="checkbox" id="checkbox2" />
<input type="checkbox" id="checkbox3" />

JavaScript

$("#dropdown").change(function() {
  var text = $('#dropdown :selected').text();
  $('#checkbox, #checkbox2, #checkbox3').prop('checked', text === 'foo');
});