counter

Creates an observable that emits incremental numbers at a specified interval. Emits 0 in the macrotask right after start() (which runs at creation unless startManually is set), then 1, 2, 3, … every interval. A subscriber added after that 0 has been emitted does not receive it.

Options

• startManually (default false): wait for start() instead of starting at creation.
• emitInitial (default true): set to false to skip the 0 emitted right after start(), so the first value is 1, one interval later. counter(ms) corresponds to RxJS timer(0, ms); counter(ms, { emitInitial: false }) corresponds to interval(ms).

Example

//  Timeline:
//
//  Time(s)   0     1     2     3     4     5
//  tick$     0     1     2     3     4     5     ...
//
//  Explanation:
//  - counter emits incrementing numbers at specified intervals
//  - Starts at 0 and continues indefinitely
//  - Useful for periodic tasks or animations

const tick$ = counter(100);

const valueHistory: number[] = [];

const subscription = tick$.subscribe((count) => {
    valueHistory.push(count);
});

await new Promise((resolve) => {
    setTimeout(resolve, 350);
});

subscription.unsubscribe();

assert.isTrue(Arr.isMinLengthArray(3, valueHistory));

assert.strictEqual(valueHistory[0], 0);

assert.strictEqual(valueHistory[1], 1);

assert.strictEqual(valueHistory[2], 2);

View source on GitHub