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feat(state): improve DX by logging undefined keys in selectSlice #852

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feat(state): improve DX by logging undefined keys in selectSlice #852

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50f69ff
feat(state): improve DX by logging undefined keys in selectSlice
mrkpks Jul 9, 2021
a587e51
Merge branch 'master' into state-operators-undefined-logs
BioPhoton Oct 3, 2021
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33 changes: 25 additions & 8 deletions libs/state/src/lib/rxjs/operators/selectSlice.ts
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Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
import { KeyCompareMap } from '../interfaces';
import { Observable, OperatorFunction } from 'rxjs';
import { filter, map } from 'rxjs/operators';
import { filter, map, tap } from 'rxjs/operators';
import { distinctUntilSomeChanged } from './distinctUntilSomeChanged';
import { isDevMode } from '@angular/core';

/**
* @description
Expand Down Expand Up @@ -82,6 +83,13 @@ export function selectSlice<T extends object, K extends keyof T>(
): OperatorFunction<T, PickSlice<T, K>> {
return (o$: Observable<T>): Observable<PickSlice<T, K>> =>
o$.pipe(
tap((state) => {
if (isDevMode() && state === undefined) {
console.warn(
'@rx-angular/state#selectSlice WARNING: state is undefined'
);
}
}),
Comment on lines +86 to +92
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Lazy state initialization is a key concept and warning for an undefined state is contradictory to that from my perspective.

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@edbzn true, lazy state is a key concept. the warning in devMode is still very helpful. especially when u are doing your first steps with rx-angular and cannot wrap your head around why selectSlice won't emit any values. The issue gets worse when your state interface has 100's of properties.

We have seen such cases, thats why the PR was opened :)

filter((state) => state !== undefined),
map((state) => {
// forward null
Expand All @@ -104,20 +112,29 @@ export function selectSlice<T extends object, K extends keyof T>(
// {str: undefined} => state.select(selectSlice(['str'])) => no emission
// {str: 'test', foo: undefined } => state.select(selectSlice(['foo'])) => no emission
if (definedKeys.length < keys.length) {
if (isDevMode()) {
const undefinedKeys = keys.filter((k) => !definedKeys.includes(k));
console.warn(
`@rx-angular/state#selectSlice WARNING: undefined value(s) of selected key(s): "${undefinedKeys.join(
'", "'
)}" selectSlice operator will return undefined`
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Technically, selectSlice will not return undefined because the next operator will filter undefined values, it will not emit any notification instead.

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agree, selectSlice won't emit any notification

);
}
return undefined;
}

// create the selected slice
return definedKeys
.reduce((vm, key) => {
vm[key] = state[key];
return vm;
}, {} as PickSlice<T, K>);
return definedKeys.reduce((vm, key) => {
vm[key] = state[key];
return vm;
}, {} as PickSlice<T, K>);
}),
filter((v) => v !== undefined),
distinctUntilSomeChanged(keys, keyCompareMap)
);
}

type PickSlice<T extends object, K extends keyof T> = Pick<T,
{ [I in K]: I }[K]>;
type PickSlice<T extends object, K extends keyof T> = Pick<
T,
{ [I in K]: I }[K]
>;