JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <select onchange="changeFirstSelect(this)">
        <option>1</option>
        <option>2</option>
        <option>3</option>
        <option>4</option>
    </select>
    <select id="second">
        <option>Please select the first option</option>
    </select>
</form>

JavaScript

var changeFirstSelect = function(element) {
	var xhr = new XMLHttpRequest();
	xhr.onreadystatechange = function() {
		if (xhr.readyState == XMLHttpRequest.DONE) {
			document.getElementById('second').innerHTML = xhr.responseText;
		}
	}
	xhr.open('GET', 'http://example.com?val1='+element.value, true);
	xhr.send(null);
}