Function getActiveElement

docs/external/js/react-dom.development.js:6764–6776

(doc)

  }

  function getActiveElement(doc) {
    doc = doc || (typeof document !== 'undefined' ? document : undefined);

    if (typeof doc === 'undefined') {
      return null;
    }

    try {
      return doc.activeElement || doc.body;
    } catch (e) {
      return doc.body;
    }
  }

  /**
   * Given any node return the first leaf node without children.