JSFiddle - React, Tailwind, and code Playground
HTML
<FORM METHOD="POST" ACTION="www.google.com" onSubmit="return buildURL(this);">
<input type="text" name="last">
<input type="text" name="first">
<input type="hidden" name="redirect" value="">
<input type="SUBMIT" name="submitButton" value="Submit">
JavaScript
function buildURL(form) {
form.redirect.value='http://www.google.com/?'+last +first;
form.action='http://www.google.com/?';
// Comment the alert and uncomment the form.submit() line
//alert('form will be posted to ' + form.action + ' redirect: ' + form.redirect.value);
// form.submit();
}