Angular: Retaining the type definition when clearing a component property

Question

Angular: Retaining the type definition when clearing a component property

Suppose a component has the following attributes:

private foo$: Observable<Array<SomeType>>;
private bar: SomeOtherType;

Eventually, they are assigned values...

this.foo$ = someSubject.pipe(switchMap(...whatever...
this.bar = new SomeOtherType(...whatever...

At a certain point, I need to clear these properties for various reasons. By clearing, I mean removing their values and setting them back to their initial state.

Setting them to undefined is not desirable as it would result in losing their "type information". It is important for TypeScript and Angular to recognize that they remain an Observable and an object of SomeOtherType.

What alternatives do I have?

angular typescript variables types undefined

Answer 1

Answer №1

To return variables to their original state before they were assigned values, simply assign them to undefined:

this.foo$ = undefined;
this.bar = undefined;

In the demonstration on StackBlitz that you used for testing, the Observable heroes$ is utilized alongside the async pipe:

<li *ngFor="let hero of heroes$ | async" >

If heroes$ is set to undefined, the list will disappear from the view and the Observable will cease functioning. The async pipe automatically unsubscribes when the component is destroyed; it seems to behave similarly when the Observable variable is set to undefined.

However, without using the async pipe with the Observable, setting the variable to undefined does not prevent the Observable from working, as demonstrated in this different example on StackBlitz.

Answer 2

To return variables to their original state before they were assigned values, simply assign them to undefined:

this.foo$ = undefined;
this.bar = undefined;

In the demonstration on StackBlitz that you used for testing, the Observable heroes$ is utilized alongside the async pipe:

<li *ngFor="let hero of heroes$ | async" >

If heroes$ is set to undefined, the list will disappear from the view and the Observable will cease functioning. The async pipe automatically unsubscribes when the component is destroyed; it seems to behave similarly when the Observable variable is set to undefined.

However, without using the async pipe with the Observable, setting the variable to undefined does not prevent the Observable from working, as demonstrated in this different example on StackBlitz.

Answer 3

Answer №2

It is my belief that you have the ability to specify the type as any, instead of leaving it undefined.

For instance, private foo$: Observable>; private bar: SomeOtherType;

Answer 4

It is my belief that you have the ability to specify the type as any, instead of leaving it undefined.

For instance, private foo$: Observable>; private bar: SomeOtherType;

Angular: Retaining the type definition when clearing a component property

Answer №1

Answer №2

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