Example of `executeAsyncJs()`

I have a case in which I request a API call via fetch/XHR (in execute async js method) grab its response and want to check that its response contains specific string.

Example:

```php
$response = $I->executeAsyncJS(<<assertContains('needle', $response);
```

I have made several attempts but unable to achieve the desired result. Sometimes I get errors or sometime empty array `[]`

It would be glad if such example is provided.

Note that there is also a [unanswered question on Stack Overflow](https://stackoverflow.com/questions/60108844/get-a-response-from-codeception-i-executeasyncjs)

Start with the executeAsyncJS() entry point and the linked Stack Overflow question to understand the expected asynchronous return value. Add a documentation example showing a fetch, XHR, or API response returned to PHP and checked with assertContains(); the example should avoid errors and empty-array results.

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