Working with layers for Node.js Lambda functions

Create the required directory structure and install packages directly into it:

mkdir -p nodejs
npm install --prefix nodejs lodash axios

This command installs the packages directly into the nodejs/node_modules directory, which is the structure that Lambda requires.

npm install --prefix nodejs --platform=linux --arch=x64 sharp

Zip the layer content:

The directory structure of your .zip file should look like this:

nodejs/
├── package.json
├── package-lock.json
└── node_modules/
 ├── lodash/
 ├── axios/
 └── (dependencies of the other packages)

Create the required directory structure for your layer:

mkdir -p nodejs/node_modules/validator
cd nodejs/node_modules/validator

Create a package.json file for your custom module to define how it should be imported:

{
 "name": "validator",
 "version": "1.0.0",
 "type": "module",
 "main": "index.mjs"
}

Create your JavaScript module file:

export function validateOrder(orderData) {
 // Validates an order and returns formatted data
 const requiredFields = ['productId', 'quantity'];
 
 // Check required fields
 const missingFields = requiredFields.filter(field => !(field in orderData));
 if (missingFields.length > 0) {
 throw new Error(`Missing required fields: ${missingFields.join(', ')}`);
 }
 
 // Validate quantity
 const quantity = orderData.quantity;
 if (!Number.isInteger(quantity) || quantity < 1) {
 throw new Error('Quantity must be a positive integer');
 }
 
 // Format and return the validated data
 return {
 productId: String(orderData.productId),
 quantity: quantity,
 shippingPriority: orderData.priority || 'standard'
 };
}
export function formatResponse(statusCode, body) {
 // Formats the API response
 return {
 statusCode: statusCode,
 body: JSON.stringify(body)
 };
}

Zip the layer content:

The directory structure of your .zip file should look like this:

nodejs/ 
└── node_modules/
 └── validator/
 ├── package.json
 └── index.mjs

In your function, import and use the modules. Example:

import { validateOrder, formatResponse } from 'validator';
export const handler = async (event) => {
 try {
 // Parse the order data from the event body
 const orderData = JSON.parse(event.body || '{}');
 
 // Validate and format the order
 const validatedOrder = validateOrder(orderData);
 
 return formatResponse(200, {
 message: 'Order validated successfully',
 order: validatedOrder
 });
 } catch (error) {
 if (error instanceof Error && error.message.includes('Missing required fields')) {
 return formatResponse(400, {
 error: error.message
 });
 }
 
 return formatResponse(500, {
 error: 'Internal server error'
 });
 }
};

You can use the following test event to invoke the function:

{
 "body": "{\"productId\": \"ABC123\", \"quantity\": 2, \"priority\": \"express\"}"
}

Expected response:

{
 "statusCode": 200,
 "body": "{\"message\":\"Order validated successfully\",\"order\":{\"productId\":\"ABC123\",\"quantity\":2,\"shippingPriority\":\"express\"}}"
}