Method _chain

test/lib/browsers/playwright.ts:672–730

(
    this: Playwright<TCurrent>,
    mustBeChained: boolean,
    nextCall: (current: TCurrent) => TNext | Promise<TNext>
  )

  readonly [Symbol.toStringTag]: string = 'Playwright'

  private _chain<TNext>(
    this: Playwright<TCurrent>,
    mustBeChained: boolean,
    nextCall: (current: TCurrent) => TNext | Promise<TNext>
  ): Playwright<TNext> & Promise<TNext> {
    const syncError = new Error('next-browser-base-chain-error')

    // If `this` is actually a proxy created by a previous chained call, it'll act like it has a `promise` property.
    // (see proxy code below)
    type MaybeChained<T> = Playwright<T> & {
      promise?: Promise<T>
    }
    const self = this as MaybeChained<TCurrent>

    let currentPromise = self.promise
    if (!currentPromise) {
      if (mustBeChained) {
        // Note that this should also be enforced by the type system
        // by adding appropriate `(this: Playwright<PreviousValue>)` type annotations
        // to methods that expect to be chained, but tests can bypass this (or not be checked because they use JS)
        throw new Error(
          'Expected this call to be chained after a previous call'
        )
      } else {
        // We're handling a call that does not expect to be chained after a previous one,
        // so it's safe to default the current value to undefined -- we don't need a value to invoke `nextCall`
        currentPromise = Promise.resolve(undefined as TCurrent)
      }
    }

    const promise = currentPromise.then(nextCall).catch((reason: unknown) => {
      // TODO: only patch the stacktrace if the sync callstack is missing from it
      if (reason && typeof reason === 'object' && 'stack' in reason) {
        const syncCallStack = syncError.stack!.split(syncError.message)[1]
        reason.stack += `\n${syncCallStack}`
      }
      throw reason
    })

    function get(target: Playwright<TCurrent>, p: string | symbol): any {
      switch (p) {
        case 'promise':
          return promise
        case 'then':
          return promise.then.bind(promise)
        case 'catch':
          return promise.catch.bind(promise)
        case 'finally':
          return promise.finally.bind(promise)
        default:
          return target[p]
      }
    }

    // @ts-expect-error: we're changing `TCurrent` into TNext via proxy hacks
    return new Proxy(this, {
      get,
    })