JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="yyyy" onkeyup="check(this.value)"></textarea>
<textarea id="xxxx" onchange="check2(this.value)" readonly></textarea>

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