code: function getPropType(propValue) {
    const propType = typeof propValue;
    if (Array.isArray(propValue)) {
      return 'array';
    }
    if (propValue instanceof RegExp) {
      // Old webkits (at least until Android 4.0) return 'function' rather than
      // 'object' for typeof a RegExp. We'll normalize this here so that /bla/
      // passes PropTypes.object.
      return 'object';
    }
    return propType;
  }
docs: Equivalent of `typeof` but with special handling for array and regexp.