JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="yyyy" oninput="check(this.value);check2(this.value)"></textarea>
<textarea id="xxxx" oninput="check2(this.value)" ></textarea>

JavaScript

function check(value){
    document.getElementById("xxxx").value = value;
}
function check2(value){
    alert(value);
}