JSFiddle - React, Tailwind, and code Playground

HTML

<textarea name="" id="myTextArea" cols="30" rows="10"></textarea>

JavaScript

let textarea = document.querySelector("#myTextArea");
let tael = textarea.addEventListener.bind(textarea);

let autoResizeTextArea = (e) => {
  const element = e.target
  element.style.height = 'auto'
  element.style.overflowY = 'hidden'
  element.style.height = element.scrollHeight + 'px'
}

tael('update', autoResizeTextArea);
tael('keyup', autoResizeTextArea);
//add event listeners for update and keyup

//for demonstration set value big enough that it will resize box:
textarea.value = `lorem Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.`;

//setup promise to resolve after 2 seconds. 
//This will simulate fetching external data.

let newPromise = new Promise((res, rej) => {
  setTimeout(() => {
    res('resolved');
  }, 2000)
}).then((success) => {

//create the update event and dispatch it
  let myEvent = new CustomEvent("update");
  textarea.dispatchEvent(myEvent);
});