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selectSlice

selectSlice

Returns an Observable that emits only the provided keys emitted by the source Observable. Each key will get filtered to only emit defined values as well as checked for distinct emissions. Comparison will be done for each set key in the keys array.

You can fine grain your distinct checks by providing a KeyCompareMap with those keys you want to compute explicitly different

Example

// An example with a custom comparison applied to each key
import { of } from 'rxjs';
import { selectSlice } from 'rx-angular/state';

const state$: Observable<MyState> = of(
{ title: 'myTitle', panelOpen: true },
{ title: 'myTitle2', panelOpen: true },
{ title: 'newTitle', panelOpen: true },
{ title: 'newTitle', panelOpen: false }
)
.pipe(selectSlice(['title', 'panelOpen']))
.subscribe((x) => console.log(x));

// displays:
// { title: 'myTitle', panelOpen: true },
// { title: 'myTitle2', panelOpen: true },
// { title: 'newTitle', panelOpen: true },
// { title: 'newTitle', panelOpen: false }

Example

import { of, Observable } from 'rxjs';
import { tap } from 'rxjs/operators';
import { selectSlice } from 'rx-angular/state';

interface MyState {
title: string;
items: string[];
panelOpen: boolean;
}
// Select items and title.
// apply custom compare logic for the items array
const customComparison: KeyCompareMap<MyState> = {
items: (oldItems, newItems) => compareItems(oldItems, newItems),
};
const state$: Observable<MyState> = of(
{ title: 'myTitle', items: ['foo', 'bar'], panelOpen: true },
{ title: 'myTitle', items: ['foo', 'bar'], panelOpen: false },
{ title: 'nextTitle', items: ['foo', 'baR'], panelOpen: true },
{ title: 'nextTitle', items: ['fooRz', 'boo'], panelOpen: false }
);
const slice$ = state$
.pipe(selectSlice(['title', 'items']), tap(console.log))
.subscribe();

// displays:
// { title: 'myTitle', items: ['foo', 'bar'] }
// { title: 'nextTitle', items: ['foo', 'baR'] }
// { title: 'nextTitle', items: ['fooRz', 'boo'] }

Signature

function selectSlice<T extends object, K extends keyof T>(
keys: K[],
keyCompareMap?: KeyCompareMap<{ [P in K]: T[P] }>
): OperatorFunction<T, PickSlice<T, K> | null>;

Parameters

keys

typeof: K[]

keyCompareMap

typeof: KeyCompareMap<{ [P in K]: T[P] }>