'then is not a function' in MongoDB Stitch Webhook - mongodb

Question

The MongoDB Stitch Webhook docs describe my precise use case: using a POST method to call insertOne then return the inserted _id.
I pasted the example below (directly from the docs) into the Stitch Function Editor.
exports = function(payload, response) {
const mongodb = context.services.get("mongodb-atlas");
const requestLogs = mongodb.db("test").collection("requestlogs");
requestLogs.insertOne({
body: EJSON.parse(payload.body.text()),
query: payload.query
}).then(result => {
response.setStatusCode(201);
response.setBody(result.insertedId);
})
};
I executed the function in the Function Editor console by calling:
exports({query: {arg1: 'hello', arg2: "world!"}, body:BSON.Binary.fromText('{"msg": "world"}')})
An error is returned indicating that .then is not a function.
error: TypeError: 'then' is not a function
Are the docs wrong, or I have I gone astray?

Answer 1

Certain methods, like .then, throw errors in the function editor. In my case, this was a shortcoming of the function editor, rather than an error in my code. Calling the webhook with fetch or Postman, the function executed as expected.
The Incoming Webhook docs contain a special note:
If you want to debug a webhook function response from the function
editor, you must manually provide the HTTP response object when you
run the function.
exports( { body: "This document is the webhook payload" }, new
HTTPResponse() )
That alerted me to the idiosyncratic nature of the function editor as a JS handler. Using Postman I confirmed the function ran without errors when called. The error generated by the function editor was a red herring.