mapOptional

Transforms the inner value of an Optional type emitted by the source. If the value is Some, the mapping function is applied; if None, it remains None.

Marble Diagram

mapOptional(x => x * 2)

Example

//  Timeline:
//
//  value$    Some(2)    None       Some(5)
//  doubled$  Some(4)    None       Some(10)
//
//  Explanation:
//  - mapOptional transforms the inner value of Optional emissions
//  - Some values are mapped; None values pass through unchanged

const value$ = source<Optional<number>>();

const doubled$ = value$.pipe(mapOptional((x) => x * 2));

const valueHistory: Optional<number>[] = [];

doubled$.subscribe((v) => {
    valueHistory.push(v);
});

value$.next(Optional.some(2));

assert.deepStrictEqual(valueHistory, [Optional.some(4)]);

value$.next(Optional.none);

assert.deepStrictEqual(valueHistory, [Optional.some(4), Optional.none]);

value$.next(Optional.some(5));

assert.deepStrictEqual(valueHistory, [
    Optional.some(4),
    Optional.none,
    Optional.some(10),
]);

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