Fix #1038 by making the AwsLambdaReceiver example TS compatible

[seratch]

Summary

This pull request fixes #1038

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #1039 (afebfcc) into main (08b50ca) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1039   +/-   ##
=======================================
  Coverage   68.89%   68.89%           
=======================================
  Files          13       13           
  Lines        1212     1212           
  Branches      357      357           
=======================================
  Hits          835      835           
  Misses        304      304           
  Partials       73       73           

Impacted Files	Coverage Δ
src/App.ts	82.91% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 08b50ca...afebfcc. Read the comment docs.

[srajiang]

Ah looks great and solves this user's issue very smoothly!

I do have a question re: when the user is instantiating their receiver separately then passing it as an option in the App constructor:

const awsLambdaReceiver = new AwsLambdaReceiver({
  signingSecret: process.env.SLACK_SIGNING_SECRET ?? ''
});

const app = new App({
  token: process.env.SLACK_BOT_TOKEN,
  processBeforeResponse: true,
  logLevel: LogLevel.DEBUG
});

In this case, would our error from #1038 still persist?

[seratch]

@srajiang

when the user is instantiating their receiver separately then passing it as an option in the App constructor:

This is the only way to use AwsLambdaReceiver so far.

In this case, would our error from #1038 still persist?

If you use app.start() method, yes. But our recommendation in TypeScript at this point is to use AwsLambdaReceiver#start() method instead.

Fixing App#start() method to be more robust may take a bit long. If we often see similar confusion around the AWS Lambda receiver, having a more specific method like AwsLambdaReceiver#toHandler() and encouraging developers not to use start() method may be an option.

[srajiang]

@seratch
Alright, that makes sense! LGTM.