Element type is invalid: expected a string (for built-in components) or a class/function

报错：

Uncaught Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports

原因：

把   default  删掉。