SyntaxError when using middleware with middy - but there is no syntax error- and custom middleware works

Question

I have a simple lambda (behind a cognito authorizer) with an http event. I am using the httpJsonParser to parse the body, then I am using a custom middleware which just validates the json using zod and last but not least I am using the httpErrorHandler middleware.

const customhandler = async (event: APIGatewayProxyEvent): Promise<APIGatewayProxyResult> => {
  return { 
    statusCode: 200,
    body: `success
    available claims  : ${JSON.stringify(event.requestContext.authorizer?.claims)}`
  };
};

export const handler = middy(customhandler)
  .use(httpJsonBodyParser())
  .use(customValidator(SOMESCHEMA))
  .use(httpErrorHandler());

The customValidator looks like this:

export const customValidator = (schema: ZodSchema): middy.MiddlewareObj<APIGatewayProxyEvent, APIGatewayProxyResult> => {
  const before: middy.MiddlewareFn<APIGatewayProxyEvent, APIGatewayProxyResult> = async (
    request
  ): Promise<void> => {
    if (request.event.body != null) {
      try {
        schema.parse(request.event.body);
      } catch (e) {
        throw new Error("Validation error");
      }
    }
  };

  return {
    before
  };
};

When I remove the .use(httpJsonBodyParser()) and the .use(httpErroHandler()) the customValidation is executed and there is no syntax error.

However as soon as I add one (or both) middlewares, with or without my custom middleware, I receive the following error when the lambda is executed:

 "Runtime.UserCodeSyntaxError: SyntaxError: Unexpected token '??='",
        "    at _loadUserApp (/var/runtime/UserFunction.js:222:13)",
        "    at Object.module.exports.load (/var/runtime/UserFunction.js:300:17)",
        "    at Object.<anonymous> (/var/runtime/index.js:43:34)",
        "    at Module._compile (internal/modules/cjs/loader.js:1085:14)",
        "    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)",
        "    at Module.load (internal/modules/cjs/loader.js:950:32)",
        "    at Function.Module._load (internal/modules/cjs/loader.js:790:12)",
        "    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:75:12)",
        "    at internal/main/run_main_module.js:17:47"

My IDE and eslint is not complaining...

As suggested, there could be an issue with the build process here is my tsconfig file:

{
  "extends": "@tsconfig/node14/tsconfig.json",
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "sourceMap": true,
    "outDir": "dist",
    "baseUrl": ".",
    "paths": {
      "core/*": [
        "../core/src/*"
      ],
      "schema/*": [
        "../schema/src/*"
      ]
    }
  }
}

nothing really special about it.

Answer 1

I upgraded to lambda node version 18.x and serverless 3 which resolved the issue.