Function waitFor

packages/private/testing/src/utils.ts:264–300

(
  callback: () => Promise<T> | T,
  options: WaitForOptions = {},
)

const realSetTimeout = setTimeout;

export async function waitFor<T>(
  callback: () => Promise<T> | T,
  options: WaitForOptions = {},
): Promise<T> {
  const waitTime = options.timeout ?? 100;
  const interval = options.interval ?? 0;
  const stack = new Error().stack;

  const deadline = realNow() + waitTime;
  let i = 0;
  let lastError: any | undefined;

  while (true) {
    try {
      return await callback();
    } catch (cause) {
      lastError = cause;
    }

    i++;

    if (deadline < realNow()) {
      throw Object.assign(
        new Error(
          `Timed out after ${waitTime}ms and ${i} attempts. ` +
            `Last error: ${lastError?.message ?? 'condition returned false'}`,
        ),
        {
          stack: stack + `Last error: ${lastError?.stack ?? 'condition returned false'}`,
        },
      );
    }

    // Guarantee a macro-task between retries.
    await new Promise((resolve) => void realSetTimeout(resolve, interval));
  }
}