Function instant

packages/next-playwright/src/index.ts:55–97

(
  page: PlaywrightPage,
  fn: () => Promise<T>,
  options?: { baseURL?: string }
)

 * as labeled steps in the Playwright UI.
 */
export async function instant<T>(
  page: PlaywrightPage,
  fn: () => Promise<T>,
  options?: { baseURL?: string }
): Promise<T> {
  // Check for nested instant() calls. The cookie is scoped to the browser
  // context, so we can detect nesting by checking if it's already set.
  const existingCookies = await page.context().cookies()
  if (existingCookies.some((c) => c.name === INSTANT_COOKIE)) {
    throw new Error(
      'An instant() scope is already active. Nesting instant() ' +
        'calls is not supported. Did you forget to await the ' +
        'previous instant() call?'
    )
  }

  // Acquire the lock by setting the cookie via the browser context. This
  // ensures the cookie is present even on the very first navigation.
  // The cookie triggers the CookieStore change event in
  // navigation-testing-lock.ts, which acquires the in-memory navigation lock.
  const { hostname } = new URL(resolveURL(page, options))
  await step('Acquire Instant Lock', () =>
    page.context().addCookies([
      {
        name: INSTANT_COOKIE,
        value: JSON.stringify([0, `p${Math.random()}`]),
        domain: hostname,
        path: '/',
      },
    ])
  )
  try {
    return await fn()
  } finally {
    // Release the lock by clearing the cookie. Next.js may have updated the
    // cookie value (e.g. from [0] to [1,null]) during the lock scope. We
    // clear by name to remove the cookie regardless of its current value or
    // which domain variant it was stored under.
    await step('Release Instant Lock', () =>
      page.context().clearCookies({ name: INSTANT_COOKIE })
    )
  }
}

/**
 * Resolves the URL to scope the instant navigation cookie to. Prefers