Mongoose Unexpected token u in JSON at position 0 - node.js

Question

I'm creating an AWS Lambda API with Node JS. There's a template for the db connection itself, but when I run a test in Lambda I get an error and I believe the problem is the connection itself.
Here's the error message I get with Lambda test:
START RequestId: 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5 Version: $LATEST
2020-05-23T01:46:23.685Z 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5 INFO => using new database connection
2020-05-23T01:46:23.689Z 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5 ERROR (node:8) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
2020-05-23T01:46:23.726Z 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5 ERROR (node:8) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
2020-05-23T01:46:23.828Z 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5 ERROR Unhandled Promise Rejection {"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"SyntaxError: Unexpected token u in JSON at position 0","reason":{"errorType":"SyntaxError","errorMessage":"Unexpected token u in JSON at position 0","stack":["SyntaxError: Unexpected token u in JSON at position 0"," at JSON.parse ()"," at /var/task/handler.js:17:22"," at processTicksAndRejections (internal/process/task_queues.js:97:5)"]},"promise":{},"stack":["Runtime.UnhandledPromiseRejection: SyntaxError: Unexpected token u in JSON at position 0"," at process. (/var/runtime/index.js:35:15)"," at process.emit (events.js:310:20)"," at processPromiseRejections (internal/process/promises.js:209:33)"," at processTicksAndRejections (internal/process/task_queues.js:98:32)"]}
END RequestId: 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5
REPORT RequestId: 6b9eef97-9c54-44bc-8ecc-dfbec7e200e5 Duration: 186.61 ms Billed Duration: 200 ms Memory Size: 1024 MB Max Memory Used: 34 MB
Unknown application error occurred
DB.js
const mongoose = require("mongoose");
mongoose.Promise = global.Promise;
let isConnected;
module.exports = connectToDatabase = () => {
if (isConnected) {
console.log("=> using existing database connection");
return Promise.resolve();
}
console.log("=> using new database connection");
return mongoose.connect(process.env.DB).then((db) => {
isConnected = db.connections[0].readyState;
});
};
Handler.js
"use strict";
const connectToDatabase = require("./db");
const Lead = require("./leads.model.js");
require("dotenv").config({ path: "./variables.env" });
module.exports.hello = (event, context, callback) => {
console.log("Hello World");
callback(null, "Hello World");
};
module.exports.create = (event, context, callback) => {
context.callbackWaitsForEmptyEventLoop = false;
connectToDatabase().then(() => {
Lead.create(JSON.parse(event.body))
.then((lead) =>
callback(null, {
statusCode: 200,
body: JSON.stringify(lead),
})
)
.catch((err) =>
callback(null, {
statusCode: err.statusCode || 500,
headers: { "Content-Type": "text/plain" },
body: "Could not create the lead.",
})
);
});
};
variables.env
DB=mongodb+srv://dbUser:password#api-jodqc.mongodb.net/test?retryWrites=true&w=majority

Answer 1

Whenever I see Unexpected token u in JSON at position 0, it usually means JSON.parse is trying to parse undefined. Looking at the code, I only see you executing parse in one spot
Lead.create(JSON.parse(event.body))
I'm guessing when you execute the Lambda, you're passing in an object that looks like a lead directly, so maybe something like below.
{
isALead: true
}
Instead, you need to test with an object that looks like
{
body: "{ \"isALead\": true }"
}