tap() isn't triggered in RXJS Pipe

问题

I have to ways of doing the same thing, although I prefer the first one. But the first approach doesn't seem to work. (the tap() is not triggered)

// does not work
this.actions$.pipe(
    ofType(LayoutActions.Types.CHANGE_THEME),
    takeUntil(this.destroyed$),
    tap(() => {
        console.log('test')
    }),
);
// works
this.actions$.ofType(LayoutActions.Types.CHANGE_THEME).subscribe(() => {
    console.log('test')
});

回答1:

Imagine RxJS pipes like actual, physical pipes with a valve at the end. Each pipe will "modify" the liquid that is flowing through it, but as long as the valve at the end is closed, nothing will ever flow.

So, what you need, is to open the valve at the end. This is done by subscribing to the observable pipe. The easiest solution is:

this.actions$.pipe(
    ofType(LayoutActions.Types.CHANGE_THEME),
    takeUntil(this.destroyed$),
    tap(() => {
        console.log('test')
    }),
).subscribe(_ => console.log("water is flowing!"));

回答2:

pipe creates new Observable thus you must asssign it and then subscribe to that isntance. In your case you are ommiting pipe return thus you end up with plain, unmodified Observable without any extra pipe actions.

Also remember that most likely you will have to subscripbe in order to pipe (and tap) to work.

try

this.actions$=this.actions$.pipe(
    tap(()=>console.log("First tap")),
    ofType(LayoutActions.Types.CHANGE_THEME),
    takeUntil(this.destroyed$),
    tap(() => {
        console.log('Last tap')
    }),
);

this.actions$.subscribe(() => {
    console.log('subscribtion')
});

来源：https://stackoverflow.com/questions/52188795/tap-isnt-triggered-in-rxjs-pipe