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JS Journey into outer space - Day 5

This article was written as part of a knowledge sharing program I created for front-end developers. It builds up to creating reusable abstractions by studying async transducers. Day 5 It's time to add more operators. We already have map , but what if the mapping function returns another "container" value, like an array or observable? 🦉 In RxJS some operators like switchMap , concatMap , or mergeMap will expect a "project" function that returns an observable (or promise or array), but what happens then? First map is applied with the project function and after that the result is "flattened". In other words: when the returned (inner) observables emit, the mapped (outer) observable emits those values instead. Since RxJs streams have a specific async behaviour the flattening process takes concurrency into account: mergeMap will flatten inner observables whenever they complete, regardless of the order, but concatMap will preserve the order of the ou...
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JS Journey into outer space - Day 4

This article was written as part of a knowledge sharing program I created for front-end developers. It builds up to creating reusable abstractions by studying async transducers. Day 4 Now we have modified transduce to handle async it's time to figure out how it can handle observables. Kickoff 🏈 First we need to pass the onNext function which kicks off the callback chain. In RxJs this is called subscribe instead, so let's rename the parameter and the callbacks to be more in line with RxJs : function transduce ( input , fn , subscribe , onError , onComplete , init ) { subscribe ( input , { next : ( cur ) => { init = fn ( init , cur ) ; } , error : ( err ) => { onError ( init , err ) ; } , complete : ( ) => { onComplete ( init ) ; } } ) ; return init ; } ; 🦉 Observables are considered a push-style of dealing with many values, while generators are pull-based. In...
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JS Journey into outer space - Day 3

This article was written as part of a knowledge sharing program I created for front-end developers. It builds up to creating reusable abstractions by studying async transducers. Day 3 Perhaps it's good to look at what was created so far and see if there's anything to improve. The code in the repo was written in a test-driven way from a data perspective, but operators and helpers remain untested at this point . Also, not all code is typed. This might become a concern if this would be a open source library with actual users, but it isn't, so just consider adding more tests and types a good exercise at generics 😀 I don't like to use alien terms but 👽 It isn't easy for me either, but we have to talk about polymorphism. We've created implementations for transducing arrays and eithers, but we're not anywhere close to dealing with observables, which is one of the aims of this project. 🦉 Polymorphism means there's a single interface that can be used for...
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JS Journey into outer space - Day 2

This article was written as part of a knowledge sharing program I created for front-end developers. It builds up to creating reusable abstractions by studying async transducers. Day 2 That's all good and nice, but wait just one moment! I'm already using RxJS (or Lodash or your framework here) and it already provides composable operator functions! You Ain't Gonna Need It? You would be right of course, and getting invested in yet another new framework for that extra bit of performance might not be worth it. However, do you need separate frameworks if there would be a single one to do all you need? Does it even exist? At first glance transducers-js looks great, but the first thing you might notice is that it hasn't been updated recently and doesn't use TypeScript. And of course we want typed functions. A nice typed functional framework is fp-ts . It's also quite complex, due to its abstract nature (if not its scarce documentation). Let's see if we can fa...
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