有关JSX

最近使用JSX遇到了一些困惑

比如下列几种情况，正确的有哪些？

1.

import * as React from 'react'
import { render } from 'react-dom'
const rootElement = document.getElementById('root')

const app = <div>I am Sally</div>

render(app, rootElement)

2.

import * as React from 'react'
import { render } from 'react-dom'
const rootElement = document.getElementById('root')

const app = () => {
  return (<div>I am Sally</div>)
}

render(app(), rootElement)