ReactRouter的实现

// line packages\react-router\modules\Router.js line 10
class Router extends React.Component {
  static computeRootMatch(pathname) {
    return { path: "/", url: "/", params: {}, isExact: pathname === "/" };
  }

  constructor(props) {
    super(props);

    this.state = {
      location: props.history.location
    };

    // This is a bit of a hack. We have to start listening for location
    // changes here in the constructor in case there are any <Redirect>s
    // on the initial render. If there are, they will replace/push when
    // they mount and since cDM fires in children before parents, we may
    // get a new location before the <Router> is mounted.
    this._isMounted = false;
    this._pendingLocation = null;

    if (!props.staticContext) {
      this.unlisten = props.history.listen(location => {
        if (this._isMounted) {
          this.setState({ location });
        } else {
          this._pendingLocation = location;
        }
      });
    }
  }

  componentDidMount() {
    this._isMounted = true;

    if (this._pendingLocation) {
      this.setState({ location: this._pendingLocation });
    }
  }

  componentWillUnmount() {
    if (this.unlisten) this.unlisten();
  }

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

我们在使用时都是使用Router来嵌套Route，所以此时就到Route组件，Route的作用是匹配路由，并传递给要渲染的组件props，Route接受上层的Router传入的context，Router中的history监听着整个页面的路由变化，当页面发生跳转时，history触发监听事件，Router向下传递nextContext，就会更新Route的props和context来判断当前Route的path是否匹配location，如果匹配则渲染，否则不渲染，是否匹配的依据就是computeMatch这个函数，在下文会有分析，这里只需要知道匹配失败则match为null，如果匹配成功则将match的结果作为props的一部分，在render中传递给传进来的要渲染的组件。Route接受三种类型的render props，<Route component>、<Route render>、<Route children>，此时要注意的是如果传入的component是一个内联函数，由于每次的props.component都是新创建的，所以React在diff的时候会认为进来了一个全新的组件，所以会将旧的组件unmount再re-mount。这时候就要使用render，少了一层包裹的component元素，render展开后的元素类型每次都是一样的，就不会发生re-mount了，另外children也不会发生re-mount。

// \packages\react-router\modules\Route.js line 17
class Route extends React.Component {
  render() {
    return (
      <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) && children.length === 0) {
            children = null;
          }

          if (typeof children === "function") {
            children = children(props);
            // ...
          }

          return (
            <RouterContext.Provider value={props}>
              {children && !isEmptyChildren(children)
                ? children
                : props.match
                  ? component
                    ? React.createElement(component, props)
                    : render
                      ? render(props)
                      : null
                  : null}
            </RouterContext.Provider>
          );
        }}
      </RouterContext.Consumer>
    );
  }
}

// packages\react-router-dom\modules\Link.js line 14
class Link extends React.Component {
  handleClick(event, history) {
    if (this.props.onClick) this.props.onClick(event);

    if (
      !event.defaultPrevented && // onClick prevented default
      event.button === 0 && // ignore everything but left clicks
      (!this.props.target || this.props.target === "_self") && // let browser handle "target=_blank" etc.
      !isModifiedEvent(event) // ignore clicks with modifier keys
    ) {
      event.preventDefault();

      const method = this.props.replace ? history.replace : history.push;

      method(this.props.to);
    }
  }

  render() {
    const { innerRef, replace, to, ...rest } = this.props; // eslint-disable-line no-unused-vars

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

          const location =
            typeof to === "string"
              ? createLocation(to, null, null, context.location)
              : to;
          const href = location ? context.history.createHref(location) : "";

          return (
            <a
              {...rest}
              onClick={event => this.handleClick(event, context.history)}
              href={href}
              ref={innerRef}
            />
          );
        }}
      </RouterContext.Consumer>
    );
  }
}

https://github.com/WindrunnerMax/EveryDay

https://zhuanlan.zhihu.com/p/44548552
https://github.com/fi3ework/blog/issues/21
https://juejin.cn/post/6844903661672333326
https://juejin.cn/post/6844904094772002823
https://juejin.cn/post/6844903878568181768
https://segmentfault.com/a/1190000014294604
https://github.com/youngwind/blog/issues/109
http://react-guide.github.io/react-router-cn/docs/guides/basics/Histories.html