rxjs utils

equalByPaths.ts

import { get } from 'lodash'

export interface EqualByProperties<TObject extends object> {
    (): (object1: TObject, object2: TObject) => boolean
    <TKey extends keyof TObject>(key: TKey): EqualByProperties<TObject>
    <TKey1 extends keyof TObject, TKey2 extends keyof TObject[TKey1]>(
        ...key: readonly [TKey1, TKey2]
    ): EqualByProperties<TObject>
    <TKey1 extends keyof TObject, TKey2 extends keyof TObject[TKey1], TKey3 extends keyof TObject[TKey1][TKey2]>(
        ...key: readonly [TKey1, TKey2, TKey3]
    ): EqualByProperties<TObject>
    <
        TKey1 extends keyof TObject,
        TKey2 extends keyof TObject[TKey1],
        TKey3 extends keyof TObject[TKey1][TKey2],
        TKey4 extends keyof TObject[TKey1][TKey2][TKey3]
    >(
        ...key: readonly [TKey1, TKey2, TKey3, TKey4]
    ): EqualByProperties<TObject>
}

const equalByProperties = (paths: ReadonlyArray<readonly PropertyKey[]> = []) => (...path: readonly PropertyKey[]) =>
    (path.length === 0
        ? (object1: object, object2: object) => paths.every(path => get(object1, path) === get(object2, path))
        : equalByProperties(paths.concat([path]))) as any
export default equalByProperties as <TObject extends object>() => EqualByProperties<TObject>

pipeBehaviorSubject.ts

import { BehaviorSubject, Observable, pipe } from 'rxjs'
import { UnaryFunction } from 'rxjs/src/internal/types'
import { map } from 'rxjs/operators'

export default function pipeBehaviorSubject<TValue, TResult>(
    subject: BehaviorSubject<TValue>,
    pipe: UnaryFunction<Observable<TValue>, Observable<TResult>>,
) {
    const piped = subject.pipe(pipe)
    let initialValue: TResult
    piped.subscribe(value => (initialValue = value)).unsubscribe()
    // @ts-ignore
    const outSubject = new BehaviorSubject(initialValue)
    piped.subscribe(outSubject)
    return outSubject
}

relay.ts

import { Subject } from 'rxjs'

export default function relay<TData>(next: (value: TData) => void): Subject<TData> {
    const subject = new Subject<TData>()
    subject.subscribe(next)
    return subject
}