1. create a folder in your local machine called nodejs
2. put your "shared" logic in that folder like /nodejs/shared.js
3. you can zip this nodejs folder and upload as a layer
4. in your lambda code require the shared.js as const shared = require('/opt/nodejs/shared.js')

Links:

• Lambda layers: https://docs.aws.amazon.com/lambda/latest/dg/configuration-layers.html
• Detailed guide: https://explainexample.com/computers/aws/aws-lambda-layers-node-app
• Using layers with SAM: https://docs.aws.amazon.com/serverlessrepo/latest/devguide/sharing-lambda-layers.html

At first, about the layer folder structure, all your shared files have to store under nodejs folder. This means, your layer will look like this:

05-24 07:09PM ~/poc/webapp-layers $ ls index.js layers node_modules package-lock.json package.json serverless.yml

~/poc/webapp-layers $ tree
...
layers/
   nodejs/
      accounts/
         index.js
...

But, with the above structure, you have to update your lambda function to require accounts modules

const accounts = require("/opt/nodejs/accounts");

If you want to use

const { accounts } = require("layers");

the structure should be:

~/poc/webapp-layers $ tree
...
layers/
   nodejs/
      node_modules/   <---------------
          layer/
             index.js
      accounts/
         index.js

And layer/index.js just re-export accounts module

"use strict";
const accounts = require("../accounts");
exports.accounts = accounts;