1.不加Switch的代码

import React, { Component } from "react";
import Div1 from "./components/div1"
import Div2 from "./components/div2"
import Page1 from "./pages/page1";
import Page2 from "./pages/page2";
import { Link, BrowserRouter, Route, NavLink } from "react-router-dom";

export default class App extends Component {
  render() {
    return (
      <div>
        <BrowserRouter>
          <NavLink activeClassName="acc" to="/a">
            a
          </NavLink>
          <NavLink activeClassName="acc" to="/b">
            b
          </NavLink>


          <Route path="/a" component={Page1} />
          <Route path="/b" component={Page2} />
          <Route path="/b" component={Page1} />
        </BrowserRouter>
        <Div1>123456789/Div1</Div1>
      </div>
    );
  }
}

1. 如果没有Switch组件，当一个path匹配到多个component时，会渲染出多个组件。一个路径在匹配到了对应的component之后，还会接着向下匹配 ，会大大的影响效率。
   

2.加了Switch组件之后

import React, { Component } from "react";
import Div1 from "./components/div1";
import Div2 from "./components/div2";
import Page1 from "./pages/page1";
import Page2 from "./pages/page2";
import { Link, BrowserRouter, Route, NavLink, Switch } from "react-router-dom";

export default class App extends Component {
  render() {
    return (
      <div>
        <BrowserRouter>
          <NavLink activeClassName="acc" to="/a">
            a
          </NavLink>
          <NavLink activeClassName="acc" to="/b">
            b
          </NavLink>

          <Switch>
            <Route path="/a" component={Page1} />
            <Route path="/b" component={Page2} />
            <Route path="/b" component={Page1} />
          </Switch>
        </BrowserRouter>
        <Div1>123456789/Div1</Div1>
      </div>
    );
  }
}

1. 将Route组件包裹在Switch组件之中，当path匹配到一个component之后，将不会再想下继续匹配，提高了程序效率。