92green-rxjs

Rxjs algorithms

Usage no npm install needed!

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README

92green-rxjs

yarn add 92green-rxjs

Rxjs algorithms.

multiCache

Accepts an array of sources (intended to be things like in-memory caches, database caches and actual data sources) and for each item attempts to retrieve the item from each source sequentially until it is found. It also saves items in caches once found. it does not guarantee item order.

import {multiCache} from '92green-rxjs';

let myMemoryCacheOperator = {
    name: 'memory-cache',
    load, // operator that loads from cache
    save, // operator that saves to cache (not needed on data source)
    clear, // operator that clears item from cache (not needed on data source)
};

// ^ all of the above operators must accept a payload of {id, item} and return {id, item}
//   item may be undefined if not known or not found

let cache = multiCache([
    myMemoryCacheOperator, // first cache
    myDatabaseCacheOperator, // deeper cache
    myDataSource // data source
])

from([
    {id: 'a'},
    {id: 'b'},
    {id: 'c'}
])
    .pipe(cache.load);

// Example output observable:

// {id: 'a', item: {id: 'a', name: 'Hi'}, source: 'data-source'}
// {id: 'b', item: {id: 'b', name: 'Hello'}, source: 'memory-cache'}
// {id: 'c', item: undefined, source: undefined}

memoryCache

An rx cache that works a lot like graphql/dataloader.

Usage with multiCache:

import {from} from 'rxjs'
import {flatMap} from 'rxjs/operators'
import {multiCache} from '92green-rxjs';
import {memoryCache} from '92green-rxjs';

let dataSource = {
    name: 'data-source',
    load: flatMap(async (payload) => ({
        ...payload,
        item: await fetch(payload.id)
    }))
};

let cache = multiCache([
    memoryCache(),
    dataSource
]);

from([
    {id: 'a'},
    {id: 'b'},
    {id: 'a'}
])
    .pipe(cache.load);


// Example output observable:

// {id: 'a', item: {id: 'a', name: 'Hi'}, source: 'data-source'}
// {id: 'b', item: {id: 'b', name: 'Hello'}, source: 'data-source'}
// {id: 'a', item: {id: 'a', name: 'Hi'}, source: 'memory-cache'}
// a is only requested once

zipDiff

Takes two observables and finds which items exist in one or both, according to a key. It emits items with matching items zipped together on an object: {a: itemA, b: itemB}, and emits unmatched items on objects with single keys like {a: itemA}, {b: itemB}.

The keyBy function is called on each item. The data returned is used as an identifier to work out when two items are matching.

A second keyBy function can be added if you need a different keyBy function for the second observable.

Items are emitted as early as they can be, so the internal buffer can try and be as small as possible. Pairs of matching items are emitted as soon as they match, and non-matching items are emitted as soon as it's known that it's impossible that there will be a match. (e.g. if the buffer contains items from A, and input observable B completes, then it's known there will never be matches for any buffered A's, so they are all emitted)

import {zipDiff} from '92green-rxjs';

zipDiff(
    obsA: Observable,
    obsB: Observable,
    keyBy: (item) => any,
    keyByB?: (item) => any
): Observable
zipDiff(obsA, obsB, itemA => itemA.id)

// obsA adds {id: "1", name: "One"}
// obsA adds {id: "2", name: "Two"}
// obsB adds {id: "3", name: "Three"}
// obsB adds {id: "2", name: "Too"}

// output:

{
    a: {id: "2", name: "Two"},
    b: {id: "2", name: "Too"}
}

{
    a: {id: "1", name: "One"}
}

{
    b: {id: "3", name: "Three"}
}

operators/bufferDistinct

Buffers items while the given predicate function returns the same thing, and emits the buffer contents when the given predicate function returns something else or the stream closes. Value comparison is performed using Object.is().

If flushObs is passed, the buffer will be flushed any time flushObs emits.

import {bufferDistinct} from '92green-rxjs/operators';

bufferDistinct(item => comparisonValue, flushObs: ?Observable)
obs.pipe(
    bufferDistinct(item => item.id)
);

// Obs adds {id: 'a', value: 1}
// Obs adds {id: 'a', value: 2}
// Obs adds {id: 'b', value: 3}
// Obs adds {id: 'c', value: 4}
// Obs adds {id: 'c', value: 5}

// output:

[
    {id: 'a', value: 1},
    {id: 'a', value: 2}
]

[
    {id: 'b', value: 3}
]

[
    {id: 'c', value: 4},
    {id: 'c', value: 5}
]

operators/complete

Emits a single item upon completion of the observable.

import {complete} from '92green-rxjs/operators';

complete()
obs.pipe(
    complete(),
    tap(() => {
        console.log("I'm done mate");
    })
);

dynamodb/batchGetWithRetry

Turns AWS DocClient.batchGet() into a pipeable observable which accepts an observable of ids and calls batchGet(), batching items to 100 at a time and retrying dynamo's UnprocessedKeys automatically.

import {batchGetWithRetry} from '92green-rxjs/dynamodb';

batchGetWithRetry({
    docClient: DocClient,
    tableName: string,
    returnItems?: boolean
}): Observable => Observable
let keys = [
    {id: 1},
    {id: 2},
    {id: 3}
];

from(keys)
    .pipe(batchGetWithRetry(...))
    .toPromise();

dynamodb/batchWriteWithRetry

Turns AWS DocClient.batchWrite() into a pipeable observable which accepts an observable of params and calls batchWrite(), batching items to 25 at a time and retrying dynamo's UnprocessedItems automatically.

import {batchWriteWithRetry} from '92green-rxjs/dynamodb';

batchWriteWithRetry({
    docClient: DocClient,
    tableName: string,
    returnItems?: boolean
}): Observable => Observable
from([{
    {
        PutRequest: {
            Item: {
                foo: 200
            }
        }
    }
    ...
}])
    .pipe(batchWriteWithRetry(...))
    .toPromise();

dynamodb/queryAll

Turns AWS DocClient.query() into an observable which will by default keep requesting whenever there is more data to be paginated.

import {queryAll} from '92green-rxjs/dynamodb';

queryAll(
    docClient: DocClient,
    params: Params,
    feedbackObservable: ?Observable
): Observable