fix(takeLast): prevent RangeError when count is Infinity

[JSap0914]

Problem

takeLast(Infinity) throws a RangeError: Invalid array length at subscription time:

// Throws: RangeError: Invalid array length
of(1, 2, 3).pipe(takeLast(Infinity)).subscribe(console.log);

The cause is line 50 of takeLast.ts:

let ring = new Array<T>(count);  // new Array(Infinity) → RangeError

JavaScript forbids creating an array with a non-integer or infinite length argument.

Fix

Use a growable array ([]) when count is non-finite. The ring-buffer index arithmetic already handles Infinity correctly because n % Infinity === n for every finite n, so no further changes to the logic are required:

let ring: T[] = isFinite(count) ? new Array<T>(count) : [];

After the fix, takeLast(Infinity) behaves like takeLast(n) where n >= source.length: it buffers every value and emits them all on completion.

Tests

Two new tests added to takeLast-spec.ts:

• Synchronous assertion that no error is thrown and all values are emitted
• Marble test verifying the observable shape matches the source

This fix was developed with AI assistance.

[Copilot]

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[ajafff]

IMO takeLast(Infinity) should be equal to identity, i.e. not changing the source sequence at all, so it needs no buffer.

On the other hand that would change the existing behavior of only emitting the items on complete to emitting immediately...

[benlesh]

Thank you for your contribution, @JSap0914.

[nx-cloud]

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☁️ Nx Cloud last updated this comment at 2026-07-22 19:59:11 UTC