类型永远不存在属性“url”？

Question

我需要订阅路由器事件：NavigationStart 和 NavigationEnd

this._router.events
        .filter(event => event instanceof NavigationStart || event instanceof NavigationEnd)
        .subscribe((event: NavigationStart | NavigationEnd) => {
            if (event instanceof NavigationStart) {
               // event.url, typescript does not flag any error
            }
            else if (event instanceof NavigationEnd) {
               // typescript flags, that property "url" does not exist on type "never".
               // if I make this block as the only block,
               // i.e. remove the previous "if" block and put this under "if"
               // then it works fine
            }
            // event.url, works fine, even here
        });

为什么 typescript 不能将 event 识别为 NavigationStart 或 NavigationEnd 的类型？虽然当我在“else if”中控制台“事件”时，我得到了“事件”的所有属性。

我见过this link1（对我不起作用）和this issue，人们给出了关闭这个问题的各种理由，design limitations。有没有我想要实现的解决方法，other than doing:

.subscribe((event: any) => {})

编辑：@Saravana 解决方案的实施

Answer 1

这是 TypeScript 编译器的一个未解决问题。见https://github.com/Microsoft/TypeScript/issues/11664

在您的情况下，您可以翻转条件以首先检查NavigationEnd。由于NavigationEnd包含NavigationStart的所有属性，编译器认为NavigationEnd的所有实例都是NavigationStart实例：

this._router.events
  .filter(event => event instanceof NavigationStart || event instanceof NavigationEnd)
  .subscribe((event: NavigationStart | NavigationEnd) => {
        if (event instanceof NavigationEnd) {

        }
        else if (event instanceof NavigationStart) {

        }
});