isFocusable.js

function isVisible(element) {
    const style = window.getComputedStyle(element);
    return style.display !== 'none';
}

function isFocusable (element) {
    const focusableElements = [
    'a[href]',
    'button:enabled',
    'input:enabled',
    'select:enabled',
    'textarea:enabled',
    'option:enabled',
    '[tabindex]:not([tabindex="-1"])'
  ];

  const focusable = focusableElements.join(', ');
  return isVisible(element) && element.matches(focusable);
}