| export type LazyResult<TValue> = PromiseLike<TValue> & { value?: TValue } | |
| export type ResolvedLazyResult<TValue> = PromiseLike<TValue> & { value: TValue } | |
| /** | |
| * Calls the given async function only when the returned promise-like object is | |
| * awaited. Afterwards, it provides the resolved value synchronously as `value` | |
| * property. | |
| */ | |
| export function createLazyResult<TValue>( | |
| fn: () => Promise<TValue> | |
| ): LazyResult<TValue> { | |
| let pendingResult: Promise<TValue> | undefined | |
| const result: LazyResult<TValue> = { | |
| then(onfulfilled, onrejected) { | |
| if (!pendingResult) { | |
| pendingResult = fn() | |
| } | |
| pendingResult | |
| .then((value) => { | |
| result.value = value | |
| }) | |
| .catch(() => { | |
| // The externally awaited result will be rejected via `onrejected`. We | |
| // don't need to handle it here. But we do want to avoid an unhandled | |
| // rejection. | |
| }) | |
| return pendingResult.then(onfulfilled, onrejected) | |
| }, | |
| } | |
| return result | |
| } | |
| export function isResolvedLazyResult<TValue>( | |
| result: LazyResult<TValue> | |
| ): result is ResolvedLazyResult<TValue> { | |
| return result.hasOwnProperty('value') | |
| } | |