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// ticker$ will update every 3s
// showHand$ will only triger after user click button
// I would like to take last ticker price as user order price when user click button
let lastPrice: number;
this.ticker$
// What I am doing now is preserve value to vairable here.
.do(ticker => lastPrice = ticker.closePrice)
.switchMap(() => this.showHand$)
.subscribe(showHand => {
// use value here
this.order.price = lastPrice;
this.order.amount = showHand.amount;
this.order.type = showHand.type;
this.submit();
});
Any segestion about how to prevser value and switch map together, without one line variable like above?
990
This map() operator is defined in a pipe where you can modify the content of emitted values from one observable to form another new observable. Inside the pipe, you can add your modification logic; in this case, it converts the emitted values to uppercase.
So here's the simple difference — switchMap cancels previous HTTP requests that are still in progress, while mergeMap lets all of them finish. In my case, I needed all requests to go through, as this is a metrics service that's supposed to log all actions that the user performs on the web page, so I used mergeMap .
Summary. We've seen that operators like map and filter are functions which take in and return observables. Each operator exposes a public function like map or filter , which is what we import from 'rxjs/operators' and pass into pipe .
Results selector function is deprecated in version 6 will be removed in version 7.
From docs:
https://github.com/ReactiveX/rxjs/blob/master/docs_app/content/guide/v6/migration.md#result-selectors
with resultSelector (v5.x)
source.pipe(
switchMap(fn1, fn2)
)
the same functionality without resultSelector, achieved with inner map
source.pipe(
switchMap((a, i) => fn1(a, i).pipe(
map((b, ii) => fn2(a, b, i, ii))
)
)
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