reactjs - React.createElement: type is invalid on Expo -

i'm starting learn react native , tried rn on expo. i'm getting error.

warning: react.createelement: type invalid -- expected string (for  built-in components) or class/function (for composite components)  got: object. forgot export component  file it's defined in. 

my code

import react 'react'; import {text, appregistry} 'react-native';  const app = () => (     <text>some text </text>     );   appregistry.registercomponent('helloworld', () => app ); 

i worte cod on app.js file

you can this:

import react, { component } 'react'; import {text, appregistry} 'react-native';  export default class app extends component {   render() {     return (       <text>hello world!</text>     );   } }   appregistry.registercomponent('helloworld', () => app );