index.ts

import * as style from './styles.css';

export interface SnackOptions {
  timeout?: number;
  actions?: string[];
}

function createSnack(message: string, options: SnackOptions): [Element, Promise<string>] {
  const {
    timeout = 0,
    actions = ['dismiss'],
  } = options;

  const el = document.createElement('div');
  el.className = style.snackbar;
  el.setAttribute('aria-live', 'assertive');
  el.setAttribute('aria-atomic', 'true');
  el.setAttribute('aria-hidden', 'false');

  const text = document.createElement('div');
  text.className = style.text;
  text.textContent = message;
  el.appendChild(text);

  const result = new Promise<string>((resolve) => {
    let timeoutId: number;

    // Add action buttons
    for (const action of actions) {
      const button = document.createElement('button');
      button.className = style.button;
      button.textContent = action;
      button.addEventListener('click', () => {
        clearTimeout(timeoutId);
        resolve(action);
      });
      el.appendChild(button);
    }

    // Add timeout
    if (timeout) {
      timeoutId = self.setTimeout(
        () => resolve(''),
        timeout,
      );
    }
  });

  return [el, result];
}

export default class SnackBarElement extends HTMLElement {
  private _snackbars: [string, SnackOptions, (action: Promise<string>) => void][] = [];
  private _processingQueue = false;

  /**
   * Show a snackbar. Returns a promise for the name of the action clicked, or an empty string if no
   * action is clicked.
   */
  showSnackbar(message: string, options: SnackOptions = {}): Promise<string> {
    return new Promise<string>((resolve) => {
      this._snackbars.push([message, options, resolve]);
      if (!this._processingQueue) this._processQueue();
    });
  }

  private async _processQueue() {
    this._processingQueue = true;

    while (this._snackbars[0]) {
      const [message, options, resolver] = this._snackbars[0];
      const [el, result] = createSnack(message, options);
      // Pass the result back to the original showSnackbar call.
      resolver(result);
      this.appendChild(el);

      // Wait for the user to click an action, or for the snack to timeout.
      await result;

      // Transition the snack away.
      el.setAttribute('aria-hidden', 'true');
      await new Promise((resolve) => {
        el.addEventListener('animationend', () => resolve());
      });
      el.remove();

      this._snackbars.shift();
    }

    this._processingQueue = false;
  }
}

customElements.define('snack-bar', SnackBarElement);