My autosize implementation

autosize_controller.js

import { Controller } from 'stimulus'

export default class extends Controller {
  initialize () {
    this.setInputAttributes()
    this.update()
  }

  update () {
    this.element.style.height = 'auto'
    this.element.style.height = `${this.element.scrollHeight}px`
  }

  setInputAttributes () {
    this.element.setAttribute(
      'style',
      `height: ${this.element.scrollHeight}px; overflow-y: hidden;`
    )
  }
}