JSFiddle - React, Tailwind, and code Playground

HTML

<input id="textbox1" />
<input id="textbox2" />

JavaScript

var textbox1 = document.getElementById("textbox1"),
    textbox2 = document.getElementById("textbox2");

textbox1.onkeydown = function () { 
    window.setTimeout(function () { textbox2.value = textbox1.value; }, 0);
}