Playwright Listen to window.PostMessages

playwright-post-message-listner.ts

```
export const setupPostMessageListener = async (page: Page) => {
  let messageList: any[] = [];

  await page.exposeFunction('publishMessagesToE2E', (message: any) => {
    messageList.push(message);
  });

  await page.evaluate(() => {
    window.addEventListener('message', (event: MessageEvent) => {
      const message = event.data;
      window.publishMessagesToE2E(message);
    });
  }, messageList);

  return {
    messageList,
    lastCalledWith: () => messageList.at(-1),
    calledTimes: () => messageList.length,
    clear: () => messageList = []
  }
}
```

You can use this as

```
const postMessageListner = await setupPostMessageListener(page);

... Do your thing

console.log(postMessageListner.messageList);
console.log(postMessageListner.calledTimes());
```

Based and inspired by https://github.com/microsoft/playwright-python/issues/1019#issuecomment-966324492 answer and https://stackoverflow.com/a/79053725/6686446