JSFiddle - React, Tailwind, and code Playground

HTML

<form name=frmregister>
    <select name=n_mode onchange="foo();">
        <option value="foo">foo</option>
        <option value="bar">bar</option>
        <option value="baz">baz</option>
    </select>
</form>

JavaScript

function foo() {
    alert(document.frmregister.n_mode.value);
}