fix(typescript-fetch): set prototype to fix instanceof not working

[petercinibulk]

Solves this issue: https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#extending-built-ins-like-error-array-and-map-may-no-longer-work

try {
    // API call
} catch (error: unknown) {
    if (error instanceof FetchError) { // Currently this will never be true
        console.log(error.message);
    }
}

@TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka @joscha

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[amakhrov]

Worth mentioning that the error only happens when your compile target is es5. Which is somewhat questionable in year 2025.

[petercinibulk]

Worth mentioning that the error only happens when your compile target is es5. Which is somewhat questionable in year 2025.

@amakhrov I am targeting ES2020 which confused me. I am also not getting an error but just not able to pass the error instanceof FetchError check.

[amakhrov]

@petercinibulk What is the exact command / params for generating the client? And how do you consume it in the app?

It sounds like you might be compiling the client as a separate library (using es5 target) and then import into your app - is it the case?

[petercinibulk]

@amakhrov You correct. However it seems like I am using the default configuration and it is generating es5 target. Should that be the default behavior?

docker run --rm \
    -v ${PWD}:/local \
    --user="$(id -u):$(id -g)" \
    openapitools/openapi-generator-cli generate \
    -i /local/openapi.json \
    -g typescript-fetch \
    -o /local/typescript \
    --additional-properties=npmName=ironpipe-client,npmVersion=$VERSION

[amakhrov]

Oh I see. It's in the tsconfig produced by the generator: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/typescript-fetch/tsconfig.mustache#L4

I would argue that supportsES6 flag should go for good. Would setting it to true in your project fix the issue you observe?

If we want to fix the generator in a backward-compatible way, we can make your changes (with prototype) conditional, based on supportsES6. But I really feel it just builds up tech debt for the mode that is long obsolete