trackThenableState

track-thenable-state.ts

export type Thenable<T> =
  | PendingThenable<T>
  | FulfilledThenable<T>
  | RejectedThenable<T>

type PendingThenable<T> = Promise<T> & { status: 'pending' }
type FulfilledThenable<T> = Promise<T> & { status: 'fulfilled'; value: T }
type RejectedThenable<T> = Promise<T> & { status: 'rejected'; reason: unknown }

export function trackThenableState<T>(promise: Promise<T>): Thenable<T> {
  // check if it's already instrumented.
  const maybeThenable = promise as Thenable<T> | Promise<T>
  if ('status' in maybeThenable && typeof maybeThenable.status === 'string') {
    return promise as Thenable<T>
  }

  const pendingThenable = promise as PendingThenable<T>
  pendingThenable.status = 'pending'
  pendingThenable.then(
    (value) => {
      const fulfilledThenable = promise as FulfilledThenable<T>
      fulfilledThenable.status = 'fulfilled'
      fulfilledThenable.value = value
    },
    (reason) => {
      const rejectedThenable = promise as RejectedThenable<T>
      rejectedThenable.status = 'rejected'
      rejectedThenable.reason = reason
    }
  )
  return promise as Thenable<T>
}