react 创建单例组件的方法

import ReactDOM from 'react-dom';/** * ReactDOM 不推荐直接向 document.body mount 元素 * 当 node 不存在时，创建一个 div */function domRender(reactElem, node) { let div; if (node) {  div = typeof node === 'string'   ? window.document.getElementById(node)   : node; } else {  div = window.document.createElement('div');  window.document.body.appendChild(div); } return ReactDOM.render(reactElem, div);}

export class SingletonLoading extends Component { globalLoadingCount = 0; pageLoadingCount = 0; state = {  show: false,  className: '',  isGlobal: undefined } delayTimer = null; start = (options = {}) => {  // ... } stop = (options = {}) => {  // ... } stopAll() {  if (!this.state.show) return;  this.globalLoadingCount = 0;  this.pageLoadingCount = 0;  this.setState({show: false}); } get isGlobalLoading() {  return this.state.isGlobal && this.state.show; } get noWaiting() {  return this.noGlobalWaiting && this.pageLoadingCount < 1; } get toPageLoading() {  return this.noGlobalWaiting && this.isGlobalLoading; } get noGlobalWaiting() {  return this.globalLoadingCount < 1; } render() {  return <BreakLoading {...this.state} />; }}// 使用上面的工具函数export const loading = domRender(<SingletonLoading />);

import loading from 'xxx';// ...loading.start();loading.stop();