Promise delegate helper

promise-delegate.ts

export type PromiseDelegateResolveCallback<ResolveType> = (value: ResolveType | PromiseLike<ResolveType>) => void

export type PromiseDelegateRejectCallback<RejectType> = (reason?: RejectType) => void

export type PromiseDelegateResult<ResolveType, RejectType> = {
  promise: Promise<ResolveType>
  resolve: PromiseDelegateResolveCallback<ResolveType>
  reject: PromiseDelegateRejectCallback<RejectType>
}

export const promiseDelegate = <ResolveType = void, RejectType = unknown>(): PromiseDelegateResult<
  ResolveType,
  RejectType
> => {
  let resolveCallback: PromiseDelegateResolveCallback<ResolveType>
  let rejectCallback: PromiseDelegateRejectCallback<RejectType>

  const promise = new Promise<ResolveType>((resolve, reject) => {
    resolveCallback = resolve
    rejectCallback = reject
  })

  return {
    promise,
    resolve: value => resolveCallback(value),
    reject: reason => rejectCallback(reason),
  }
}