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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$)
.subscribe(showHand => {
// use value here
this.order.price = lastPrice;
this.order.amount = showHand.amount;
this.order.type = showHand.type;
this.submit();
});
Any segestion about how to prevser value and switch map together, without one line variable like above?
// ticker$ 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$)
.subscribe(showHand => {
// use value here
this.order.price = lastPrice;
this.order.amount = showHand.amount;
this.order.type = showHand.type;
this.submit();
});
Any segestion about how to prevser value and switch map together, without one line variable like above?
Share Improve this question asked Sep 25, 2017 at 4:57 Long ZhaoLong Zhao 1531 gold badge1 silver badge9 bronze badges 1- 1 Please consider changing the accepted answer to the result selector solution posted by Cameron. There is no need to use another operator and withLatestFrom has certain caveats. – Christof Commented Oct 24, 2019 at 7:41
4 Answers
Reset to default 15Results selector function is deprecated in version 6 will be removed in version 7.
From docs:
https://github.com/ReactiveX/rxjs/blob/master/docs_app/content/guide/v6/migration.md#result-selectors
with resultSelector (v5.x)
source.pipe(
switchMap(fn1, fn2)
)
the same functionality without resultSelector, achieved with inner map
source.pipe(
switchMap((a, i) => fn1(a, i).pipe(
map((b, ii) => fn2(a, b, i, ii))
)
)
The behaviour you require is already possible with an overload of SwitchMap with a selectorFunc for the combination of every (outerValue,innerValue):
this.ticker$
.switchMap(
() => this.showHand$,
(tickerValue, switchMap) => tickerValue
)
.subscribe(showHand => { });
There is a little hack to achieve this - basically you have a whole new observable inside the switchmap, and this observable has access to the value passed into the switchmap function. You can use this value in an inner map to preserve the value.
this.ticker$
.switchMap(ticker => this.showHand$.pipe(map(hand => ({ ticker,hand }) ))
.subscribe( obj => {
// use value here
this.order.price = obj.ticker;
this.order.amount = obj.hand.amount;
this.order.type = obj.hand.type;
this.submit();
});
I think this is the operator
this.showHand$.take(1)
.withLatestFrom(this.ticker$)
.subscribe(([showHand, ticker]) => {
this.order.price = ticker.closePrice;
this.order.amount = showHand.amount;
this.order.type = showHand.type;
this.submit();
});
Note, take(1) will close subscription, but if you want the user to be able to press the button many times, save the subscription to a const and unsubscribe when finished.
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