appsync: error destructuring within function signature in JS resolver runtime (TypeScript)

[berkzorlu]

Describe the bug

When using JS resolver pipelines with TS, I have encountered an unexpected error in my code.

If:

• we have a props object containing optional parameters
• we destructure that object within the function signature
• and a usage of this function does not provide the optional parameter

The deployment results in an error.

My tsconfig settings are identical to the ones recommended on https://docs.aws.amazon.com/appsync/latest/devguide/resolver-reference-overview-js.html#working-with-typescript but the transpiled js is still troublesome to the js runtime.

Expected Behavior

I expect the JS resolver code to deploy without errors.

Current Behavior

The deployment results in an error.

Reproduction Steps

export type Props = {
	s: string;
	o?: string;
};

export const test = ({ s, o }: Props): void => {
	util.appendError(`${s}${o}`, 'type');
};

And we call this function without providing the optional property:

test({ s: 'test' });

The transpiled js file looks like this:

// src/test.ts
var test = ({ s, o }) => {
  util.appendError(`${s}${o}`, "type");
};
export {
  test
};

This is reproducible every time when the object parameter contains an optional property and at least one usage of this function does not provide the optional property.

Possible Solution

The error goes away if we destructure inside the function rather than the function signature:

export type Props = {
	s: string;
	o?: string;
};

export const test = (props: Props): void => {
	const { s, o } = props;
	util.appendError(`${s}${o}`, 'type');
};

Additional Information/Context

No response

CDK CLI Version

n/a

Framework Version

SST v2.8.27

Node.js Version

n/a

OS

mac

Language

Typescript

Language Version

No response

Other information

No response

[peterwoodworth]

Hey @berkzorlu, I'm a bit confused. What does this have to do with CDK?

[berkzorlu]

Hey @berkzorlu, I'm a bit confused. What does this have to do with CDK?

Hmm I think you're right. It's more of a potential issue with the JS resolver runtime in combination with the recommended TS configuration, and that probably doesn't belong here since the same result is achievable if we deployed the resolver manually through the AWS console.

What might be the proper channel to report this?

[peterwoodworth]

I'm not sure the specific error you're getting, or if you can or are supposed to work around your error by modifying the tsconfig. The best place would be premium support if you have it, else I'd recommend asking Stack Overflow, or something like repost

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