function cloneElement(element, config, children) {
    if (element === null || element === undefined) {
      throw new Error("React.cloneElement(...): The argument must be a React element, but you passed " + element + ".");
    }

    var propName; // Original props are copied

    var props = assign({}, element.props); // Reserved names are extracted

    var key = element.key;
    var ref = element.ref; // Self is preserved since the owner is preserved.

    var self = element._self; // Source is preserved since cloneElement is unlikely to be targeted by a
    // transpiler, and the original source is probably a better indicator of the
    // true owner.

    var source = element._source; // Owner will be preserved, unless ref is overridden

    var owner = element._owner;

    if (config != null) {
      if (hasValidRef(config)) {
        // Silently steal the ref from the parent.
        ref = config.ref;
        owner = ReactCurrentOwner.current;
      }

      if (hasValidKey(config)) {
        {
          checkKeyStringCoercion(config.key);
        }

        key = '' + config.key;
      } // Remaining properties override existing props


      var defaultProps;

      if (element.type && element.type.defaultProps) {
        defaultProps = element.type.defaultProps;
      }

      for (propName in config) {
        if (hasOwnProperty.call(config, propName) && !RESERVED_PROPS.hasOwnProperty(propName)) {
          if (config[propName] === undefined && defaultProps !== undefined) {
            // Resolve default props
            props[propName] = defaultProps[propName];
          } else {
            props[propName] = config[propName];
          }
        }
      }
    } // Children can be more than one argument, and those are transferred onto
    // the newly allocated props object.


    var childrenLength = arguments.length - 2;

    if (childrenLength === 1) {
      props.children = children;
    } else if (childrenLength > 1) {
      var childArray = Array(childrenLength);

      for (var i = 0; i < childrenLength; i++) {
        childArray[i] = arguments[i + 2];
      }

      props.children = childArray;
    }

    return ReactElement(element.type, key, ref, self, source, owner, props);
  }
Clone and return a new ReactElement using element as the starting point.
See https://reactjs.org/docs/react-api.html#cloneelement