Poor man's form button progress indicator, in Stimulus, for those long processing requests.

button_progress_controller.js

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  connect() {
    addEventListener("turbo:submit-end", ({ target }) => {
      clearInterval(this.interval);
      this.element.innerHTML = this.originalLabel;
    })
    this.originalLabel = this.element.innerHTML;
  }

  click(event) {
    let button = event.target;
    button.innerHTML = '...';
    
    // Remove the label from the button
    let labelStates = [
      '•..', '••.', '•••',
      '.••', '..•', '...'
    ];
    
    let currentIndex = 0;
    this.interval = setInterval(() => {
      button.innerHTML = labelStates[currentIndex];
      currentIndex = (currentIndex + 1) % labelStates.length;
    }, 500);
  }

  disconnect() {
    clearInterval(this.interval);
  }
}