Using serverless deployment to lambda with ES6 /Node.js v16 - node.js

Question

Newbie question....
I have a locally working node.js application which I am now trying to deploy express to AWS lambda. I have used this guide to deploy a test version (which worked).
I now am trying to implement my application which uses ES6 (and has type: module in package.json).
In my application I have added
import serverless from 'serverless-http'
but I cannot figure out the appropriate syntax for the export - the original was...
module.exports.handler = serverless(app);
I have tried:
const handler = async (app) =\> {
return serverless(app)
}
export default handler
Error message received:
2022-11-05T15:50:25.962Z undefined ERROR Uncaught Exception
"errorType": "Runtime.HandlerNotFound",
"errorMessage": "app.handler is undefined or not exported",
"stack": [
"Runtime.HandlerNotFound: app.handler is undefined or not exported",
" at Object.UserFunction.js.module.exports.load (file:///var/runtime/index.mjs:979:15)",
" at async start (file:///var/runtime/index.mjs:1137:23)",
" at async file:///var/runtime/index.mjs:1143:1"
]
I strongly suspect I am missing some fundamental understanding - truly appreciate some guidance.

Answer 1

The reason for the error is that you are sending a default export when AWS Lambda is expecting a named export.
The issue is the same as with all ES6 imports/exports:
// export.js
export default const defaultExport = "foo"
export const namedExport = "bar"
// import.js
import { defaultExport } from "./export.js" // error, cannot find defaultExport
import { namedExport } from "./export.js" // success, found namedExport
import defaultExport from "./export.js" // success, found defaultExport
So, it's like the case above where you're sending the defaultExport, but AWS Lambda wants the { namedExport }. You just need to remove default from your export, and make sure you're building the handler properly. Here is a suggestion to do that:
const lambda = serverless(app)
export async function handler(event, context) {
return lambda(event, context)
}
I've tested and it's working with serverless-offline using Node18.x. You can read more about exports on MDN.