关于react-router

一、先问两个问题

• 哈希路由跳转时参数拼在哪里？

  https://xxx.com/xxx/#/home?a=1&b=2

  https://xxx.com/xxx/?a=1&b=2#/home

• 区别和优缺点在哪里？

---

• 完整的URL由这几个部分构成：scheme://host:port/path?query#hash

  • scheme：通信协议，常用的有http、https、ftp、mailto等。
  • host：主机域名或IP地址。
  • port：端口号，可选。省略时使用协议的默认端口，如http默认端口为80。
  • path：路径由零或多个”/“符号隔开的字符串组成，一般用来表示主机上的一个目录或文件地址。
  • query：查询，可选。用于传递参数，可有多个参数，用”&“符号隔开，每个参数的名和值用”=”符号隔开。
  • hash：信息片断字符串，也称为锚点。用于指定网络资源中的片断。

二、react-router是怎么跳转的

1. react-router的一般用法

   import { HashRouter, Route, Switch } from 'react-router-dom';
      <HashRouter>
        <Switch>
          <Route path='/' component={Home}/>
          <Route path='/list' render={() => <List />}/>
   <Route path='/detail'><Detail /><Route>
        </Switch>
      </HashRouter>

2. react-router-dom和react-router什么关系
   看下react-router目录:

   export { default as MemoryRouter } from "./MemoryRouter.js";
   export { default as Prompt } from "./Prompt.js";
   export { default as Redirect } from "./Redirect.js";
   export { default as Route } from "./Route.js";
   export { default as Router } from "./Router.js";
   export { default as StaticRouter } from "./StaticRouter.js";
   export { default as Switch } from "./Switch.js";
   export { default as generatePath } from "./generatePath.js";
   export { default as matchPath } from "./matchPath.js";
   export { default as withRouter } from "./withRouter.js";
   
   export { default as __HistoryContext } from "./HistoryContext.js";
   export { default as __RouterContext } from "./RouterContext.js";
   
   export { useHistory, useLocation, useParams, useRouteMatch } from "./hooks.js";

   react-router-dom目录:

   export {
     MemoryRouter,
     Prompt,
     Redirect,
     Route,
     Router,
     StaticRouter,
     Switch,
     generatePath,
     matchPath,
     withRouter,
     useHistory,
     useLocation,
     useParams,
     useRouteMatch
   } from "react-router";
   
   export { default as BrowserRouter } from "./BrowserRouter.js";
   export { default as HashRouter } from "./HashRouter.js";
   export { default as Link } from "./Link.js";
   export { default as NavLink } from "./NavLink.js";

• react-router: 实现了路由的核心功能
• react-router-dom: 基于react-router，加入了在浏览器运行环境下的一些功能
  例如：
  • Link组件，会渲染一个a标签，Link组件源码a标签行;
  • BrowserRouter和HashRouter组件，前者使用pushState和popState事件构建路由，后者使用 window.location.hash和hashchange事件构建路由。
    

2.1 BrowserRouter和HashRouter

import { Router } from "react-router";
import { createHashHistory as createHistory } from "history";
class HashRouter extends React.Component {
  history = createHistory(this.props);

  render() {
    return <Router history={this.history} children={this.props.children} />;
  }
}

• createBrowserHistory 和 createHashHistory
• setState、PopStateEvent、HashChangeEvent、replaceHashPath（为什么hash后面的参数不被保留）

2.2 Router

<RouterContext.Provider
        value={{
          history: this.props.history,
          location: this.state.location,
          match: Router.computeRootMatch(this.state.location.pathname),
          staticContext: this.props.staticContext
        }}
      >
        <HistoryContext.Provider
          children={this.props.children || null}
          value={this.props.history}
        />
      </RouterContext.Provider>

2.3 Switch

<RouterContext.Consumer>
        {context => {
          invariant(context, "You should not use <Switch> outside a <Router>");
          const location = this.props.location || context.location;
          let element, match;

          // We use React.Children.forEach instead of React.Children.toArray().find()
          // here because toArray adds keys to all child elements and we do not want
          // to trigger an unmount/remount for two <Route>s that render the same
          // component at different URLs.
          React.Children.forEach(this.props.children, child => {
            if (match == null && React.isValidElement(child)) {
              element = child;
              const path = child.props.path || child.props.from;
              match = path
                ? matchPath(location.pathname, { ...child.props, path })
                : context.match;
            }
          });
          return match
            ? React.cloneElement(element, { location, computedMatch: match })
            : null;
        }}
      </RouterContext.Consumer>

2.4 Route（children, component, render 三种render方式）

<RouterContext.Consumer>
        {context => {
          invariant(context, "You should not use <Route> outside a <Router>");

          const location = this.props.location || context.location;
          const match = this.props.computedMatch
            ? this.props.computedMatch // <Switch> already computed the match for us
            : this.props.path
            ? matchPath(location.pathname, this.props)
            : context.match;

          const props = { ...context, location, match };

          let { children, component, render } = this.props;

          // Preact uses an empty array as children by
          // default, so use null if that's the case.
          if (Array.isArray(children) && isEmptyChildren(children)) {
            children = null;
          }

          return (
            <RouterContext.Provider value={props}>
              {props.match
                ? children
                  ? typeof children === "function"
                    ? __DEV__
                      ? evalChildrenDev(children, props, this.props.path)
                      : children(props)
                    : children
                  : component
                  ? React.createElement(component, props)
                  : render
                  ? render(props)
                  : null
                : typeof children === "function"
                ? __DEV__
                  ? evalChildrenDev(children, props, this.props.path)
                  : children(props)
                : null}
            </RouterContext.Provider>
          );
        }}
      </RouterContext.Consumer>

从源码我们可以看到：

• Route 的 component，render，children 三个属性是互斥的
• 优先级 children>component>render
• children 在无论路由匹配与否，都会渲染
  
  三、V6版本更新内容
  Upgrading from v5 v6.3.0 | React Router