react学习系列6 react-router 实现异步按需加载模块

import React from 'react'
import { BrowserRouter as Router, Route, Link, Switch } from 'react-router-dom'
import Home   from '$pages/Home/'
import List   from '$pages/List/'
// import City   from '$pages/City/'
// import Login  from '$pages/Login/'
import Detail from '$pages/Detail/'
import Search from '$pages/Search/'
import UserCenter  from '$pages/UserCenter/'
import Demo   from '$pages/Demo/'
import NoMatch from './404'

// 异步按需加载component
function asyncComponent(getComponent) {
  return class AsyncComponent extends React.Component {
    static Component = null;
    state = { Component: AsyncComponent.Component };

    componentWillMount() {
      if (!this.state.Component) {
        getComponent().then(({default: Component}) => {
          AsyncComponent.Component = Component
          this.setState({ Component })
        })
      }
    }
    render() {
      const { Component } = this.state
      if (Component) {
        return <Component {...this.props} />
      }
      return null
    }
  }
}

function load(component) {
  return import(`$pages/${component}/`)
}

const Login = asyncComponent(() => load('Login'));
const City = asyncComponent(() => load('City'));

export class RouterMap extends React.Component {
  render() {
    return (
      <Router>
        <div>
          { /*
          <ul>
            <li><Link to="/">Home</Link></li>
            <li><Link to="/list">List</Link></li>
          </ul>
          <hr/>
          */ }
          <Switch>
            <Route exact path="/" component={Home} />
            <Route path="/login/:refer?" component={Login} />
            <Route path="/city" component={City} />
            <Route path="/user" component={UserCenter} />
            <Route path="/list" component={List} />
            <Route exact path="/demo" component={Demo} />
            <Route path="/search/:category/:keyword?" component={Search} />
            <Route path="/detail/:id" component={Detail} />
            <Route component={NoMatch}/>
          </Switch>
        </div>
      </Router>
    );
  }
}