fig-4.js

const createProxyHttpResponse = ({ statusCode, key, message }) => ({
  statusCode,
  body: JSON.stringify({ key, message }),
  headers: { 'Content-Type': 'application/json' },
});

const formatErrorForApiGateway = async ({ error,  callback }) =>
  callback(
    null,
    createProxyHttpResponse(
      error instanceof CustomError
        ? error
        // Catch non-custom errors
        : new InternalServerError({ message: error.message })
    )
  );
  
const businessLogic = async () => {
  ...
  throw new BadRequestError({
    key: "INVALID_TOMATO_COLOR",
    message: "Tomatoes should be red"
  })
  ...
};

const myHandler = middy(businessLogic)
  .onError(formatErrorForApiGateway);