Run Promise Tasks with Bounded Concurrency

Problem Statement

In simulation dashboards and autonomous vehicle teleoperation tools, frontend clients often need to fetch dozens of assets or telemetry chunks without overwhelming the browser's network pool or backend endpoints.

Implement a function mapConcurrentSettled that executes an array of asynchronous task factories with a strict upper bound on concurrency.

Requirements

1. Validation: If concurrency is not an integer or is less than 1, reject immediately with a RangeError.
2. Execution Cap: At any point in time, no more than concurrency task factories may be actively executing.
3. Single Execution: Each task factory must be invoked exactly once.
4. No Fail-Fast: Execution must continue until all tasks have settled. A failure in one task must not abort remaining tasks.
5. Sync & Async Errors: A task factory that throws synchronously must be captured as a rejection rather than halting the runner.
6. Order Preservation: The returned promise resolves to an array of PromiseSettledResult objects, ordered to match the original tasks input order.

Interface

type PromiseSettledResult =
  | { status: 'fulfilled'; value: T }
  | { status: 'rejected'; reason: unknown };

type TaskFactory = () => Promise | T;

function mapConcurrentSettled(
  concurrency: number,
  tasks: TaskFactory[]
): Promise[]>;

Constraints

• tasks.length is between 0 and 10,000.
• concurrency is an integer `1 new Promise((resolve) => setTimeout(() => resolve('A'), 50)), () => Promise.reject(new Error('Network error')), () => { throw new Error('Sync fail'); }, () => 'B' ];

const results = await mapConcurrentSettled(2, tasks); // Output: // [ // { status: 'fulfilled', value: 'A' }, // { status: 'rejected', reason: Error('Network error') }, // { status: 'rejected', reason: Error('Sync fail') }, // { status: 'fulfilled', value: 'B' } // ]

### Example 2

```typescript
await mapConcurrentSettled(0, [() => Promise.resolve(1)]);
// Rejection: RangeError("concurrency must be an integer >= 1")

Edge Cases

• Empty tasks array: Resolve immediately to [].
• concurrency >= tasks.length: All tasks start immediately.
• Task returns a non-promise value (e.g. primitive T): Must be handled as a resolved promise.