问题
I'm trying to setup a simple error notifications component, whilst debugging in Visual Studio, within subscribe, this appears to be undefined.
public notifications: NotificationMessage[];
constructor(notificationService: NotificationService) {
this.notifications = []; //'this' is defined here
notificationService.rxEmitter.subscribe((notificationMessages: any) => {
this.notifications = notificationMessages; //'this' is undefined here
});
}
Edit : Screenshot of this being undefined from a breakpoint in VS. Interestingly, '_this', does exist at runtime, though I can't reference it as typescript throws an reference not found error on compilation.
回答1:
It turns out Visual Studios debugger was giving me a red herring saying this is undefined. Testing it out with console.log gave a valid output.
Visual Studio has trouble with arrow functions. Typescript compiles this to _this.
If you create a breakpoint from within subscribe and inspect this, Visual Studios debugger will be inspecting the anonymous function in the generated javascript code above and can no longer find this.
A workaround is to inspect _this instead.
This article seems to describe my issue.
https://typescript.codeplex.com/workitem/1655
来源：https://stackoverflow.com/questions/45566506/rxjs-why-is-this-undefined-within-subscribe