gistfile1.txt

//
<div data-controller="required-field" data-required-field-message="Email is required">
  <input name="email" data-target="required-field.field" ...>
</div>

<div data-controller="required-field" data-required-field-message="Password is required">
  <input name="password" data-target="required-field.field">
</div>

//
import { Controller } from "stimulus"

export default class extends Controller {
  static targets = [ "field" ]

  validate() {
    if (this.fieldTarget.value.length < 1) {
      this.element.appendChild(`<p class='warning'>${this.data.get("message")}</p>`
    }
  }
}