JSFiddle - React, Tailwind, and code Playground

HTML

<form id="formA" action="John/Doe" method="post">
    <select name="Letters" id="Letters">
        <option value="1">A</option>
        <option value="2">B</option>
        <option value="3">C</option>
        <option value="4">D</option>
    </select>
</form>

JavaScript

$(document).on('change', '#Letters', function() {
	alert("Would submit here")
});

$.post("/echo/json", {
  json: JSON.stringify({newValue: 3})
}, "json").done(({ newValue }) => {
	$("#Letters").val(newValue) // should select "C"
})