There should be a Promise.isThenable or Promise.is. Strictly speaking this library checks if a value is a thenable. With optional chaining I would however use

There should be a Promise.isThenable or Promise.is. Strictly speaking this library checks if a value is a thenable. With optional chaining I would however use this check: typeof x?.then === 'function' Or if I was code golfin: x?.then?.call The first case does not account for built in prototype extensions and the second has false positives with certain data structures. So the function in is-promise should be available as Promise.isThenable or Promise.is.