selectFile() - Shows the file selector dialog and returns an array of the selected files.

selectFile.js

/**
 * Shows the file selector dialog and returns an array of the selected files.
 * @param {?selectFile__Options=} options
 * @returns {Promise<File[]>}
 */
function selectFile(options) {
  return new Promise(resolve => {
    function onClose(e) {
      resolve([...e.target.files]);
    }
    Object.assign(document.createElement('input'), {
      type: 'file',
      accept: options?.accept?.join(', '),
      multiple: options?.multiple ?? false,
      onchange: onClose,
      oncancel: onClose,
    }).click();
  });
}
/**
 * @typedef selectFile__Options
 * @property {?string[]=} accept
 *   Optional array of acceptable file types (e.g., ['.jpg', '.png']).
 * @property {?boolean=} multiple
 *   Defaults to `false`.  Whether to allow selecting multiple files.
 */