# Checks with async IIFE reporting success incorrectly

> Changes related to additional security measures for Browser checks changed the default behavior of the runner.

Source: https://www.checklyhq.com/blog/post-mortem-checks-with-async-iife-reporting-success-incorrectly/

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[Blog](https://www.checklyhq.com/blog/)

# Post mortem: checks with async IIFE reporting success incorrectly

[Umut Uzgur](https://www.checklyhq.com/blog/author/umut/)

June 15, 2020 · Updated January 12, 2024

Between 05.06.2020-12.06.2020, checks using the async IIFE syntax had runs marked as passed when, in reality, they were not correctly executed.

**Impact**

We detected 18 active checks which were affected.

**Root Causes**

Changes related to additional security measures for Browser checks changed the default behavior of the runner. These changes affected the way we handle promises which are not awaited or returned.

**Resolution**

Instead of exiting the process when the execution block was finished, we let the node process exit after it executed all promises.

**Detection**

A customer contacted us after their checks didn't detect an outage they were having.

### What Are We Doing About This?

- We pushed the fix immediately on Friday after it was reported.
- We added fixtures to our test suite with async IIFE syntax and added checks to staging and production suites.
- We set up paging capabilities to these checks in case anything avoids our unit tests.

## Timeline

05.06.2020

- 12:00 security changes were rolled out to half of the regions

08.06.2020

- 11:00 security changes were rolled out to all regions

12.06.2020

- 15:03 We got informed by a customer that their tests were passing without printing certain logs
- 15:13 We found the root cause of the issue and offered the customer a workaround
- 15:30 We implemented a quick fix for the issue
- 18:30 After talking to the customer, we decided that the issue had to be resolved ASAP
- 19:00 We started testing the fix
- 19:20 We pushed the fix to production and started observing the stats
- 20:00 We declared the incident resolved

[Umut Uzgur Senior Engineering Team Lead](https://www.checklyhq.com/blog/author/umut/)

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