核心在于使用React的接口React.createPortal(element, domContainer)。该接口将element渲染后的DOM节点嵌入domContainer(通常是document.body)，并保证只嵌入一次。
所以，我们可以这样写一个对话框或模态框：
function Dialog() { return React.createPortal( <div>Dialog contents</div>, document.body ) }
一个新的div会出现在body内部：
一个完整DEMO:
class Modal extends React.Component { render() { const { visible, onClose } = this.props return visible && ReactDOM.createPortal(<StyledModalRoot> <div className="box"> Content <br/> <button onClick={onClose}>Close</button> </div> </StyledModalRoot>, document.body) } } class App extends React.Component { state = { visibleModal: false } showModal = () => this.setState( { visibleModal: true } ) handleCloseModal = () => this.setState( { visibleModal: false } ) render() { const { visibleModal } = this.state return <div style={{padding: '20px'}}> <button onClick={ this.showModal }>Show Modal</button> <Modal visible={visibleModal} onClose={ this.handleCloseModal } /> </div> } } const StyledModalRoot = styled.div` position: fixed; z-index: 1001; left: 0; top: 0; display: grid; place-items: center; width: 100%; height: 100%; background: rgba( 0, 0, 0, 0.2 ); >.box { position: relative; display: grid; place-items: center; width: 80%; height: 80%; background: white; border-radius: 10px; box-shadow: 0px 3px 5px -1px rgba(0,0,0,0.2), 0px 5px 8px 0px rgba(0,0,0,0.14), 0px 1px 14px 0px rgba(0,0,0,0.12); } `