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Let's consider the following simplified situation:
I want to filter the apples observable such that the rotten apples don't pass the filter. More precisely, an apple A passes the filter if and only if the first item emitted by A.isRotten() is false. What is the best way to implement this filter?
After some thinking I could come up with this:
apples
.concatMap(apple =>
apple.isRotten()
.first()
.filter(bool => bool)
.map(bool => apple))
Which is written in javascript. ( ... => ... is a function). This works, but I think it is rather lengthy and difficult to understand. Is there a better way to do this kind of thing?
639
The RxJS filter() operator is like the well-known Array Array . prototype. filter() method. This operator takes values from the source Observable, passes them through a predicate function and only emits those values that get TRUE.
This operator will filter the values from source Observable based on the predicate function given.
Subscribinglink An Observable instance begins publishing values only when someone subscribes to it. You subscribe by calling the subscribe() method of the instance, passing an observer object to receive the notifications.
The Filter Operator in Angular filters the items emitted by the source Observable by using a condition (predicate). It emits only those values, which satisfies the condition and ignores the rest.
What you've got is fine and, tbh, I can't think of a more concise way of doing it. I'd probably use flatMap rather than concatMap if out-of-order apples aren't an issue.
If readibility is an issue for you, just move the implementation into it's one function (eg. filterObservable that accepts a function that takes a value and returns an IObservable<bool>)
107
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