Promise Patterns

What does Promise.withResolvers() return, and what problem does it solve? Show the deferred pattern with and without it.

What are the most common Promise anti-patterns, and what does the correct code look like in each case?

Implement a withTimeout(promise, ms) helper and a retry(fn, options) helper with exponential backoff. What edge cases do production implementations need to handle?

How do you cancel an in-flight async operation with AbortController and AbortSignal? Show integration with fetch, signal composition, and how to adapt non-aware APIs.

When does a .then callback actually run relative to surrounding code? Walk through the microtask queue and how await desugars to a microtask checkpoint.

Implement a MyPromise class whose then method follows the Promises/A+ state machine: a promise starts pending and transitions once to fulfilled or rejected; then callbacks run asynchronously (on the microtask queue) and must chain; and a handler that returns another promise is adopted.