https://github.com/hermanbanken/rx-splice

https://github.com/hermanbanken/rx-splice

Last synced: 6 months ago
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• Host: GitHub
• URL: https://github.com/hermanbanken/rx-splice
• Owner: hermanbanken
• Created: 2018-06-25T12:47:14.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2018-06-25T14:04:11.000Z (over 7 years ago)
• Last Synced: 2025-03-25T20:13:07.176Z (7 months ago)
• Language: TypeScript
• Homepage:
• Size: 37.1 KB
• Stars: 5
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
RxJS splice operator

----

This package offers the RxJS splice operator: an eager variant of the `groupBy` operator.

Usage:

````typescript

import { splice } from "rx-splice";

const input$ = Observable.from("a-value", "b-value", "c-value", /* more... */);

const spliced = splice(input$, (value: string) => value[0]);

spliced("a").subscribe(console.log);

spliced("b").subscribe(console.log);

// etc

````

# Rationale

Using only idiomatic RxJS code, one would use `filter` instead for the use case of `splice`.

However, if you are writing high performance code and this `input$` Observable above

(or more likely, Subject) would be subscribed hunderths or thousands of times (X),

and thus the selector function of `filter(fn)` would be called X times.

This can - and actually did prove to - be the biggest performance bottleneck in our application,

so we wrote `splice`, which executes it's indexing selector only once for each emitted value.

Note that `splice` operates like `share` in how it subscribes upstream:

- subscribing the _first_ 'shard' will active the upstream subscription,

- later subscriptions wont trigger additional upstream subscriptions and

- unsubscribing the _last_ subscription will unsubscribe the upstream subscription too.