take

ソース Observable の最初の n 個の発行のみを取得し、完了します。

Marble Diagram

take(3)

使用例

//  Timeline:
//
//  num$    1     2     3     4 (ignored)
//  taken$  1     2     3     | (completes)
//
//  Explanation:
//  - take emits only the first n values, then completes
//  - Subsequent emissions from the source are ignored

const num$ = source<number>();

const taken$ = num$.pipe(take(3));

const valueHistory: number[] = [];

taken$.subscribe((x) => {
    valueHistory.push(x);
});

num$.next(1);

num$.next(2);

num$.next(3);

assert.deepStrictEqual(valueHistory, [1, 2, 3]);

num$.next(4); // ignored (already completed)

assert.deepStrictEqual(valueHistory, [1, 2, 3]);

View source on GitHub