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AWS Lambda Shim

The AWS Lambda Shim library is available on GitHub.

CircleCI npm

A Better Lambda API

This library provides an abstraction between the AWS Lambda events and classic node.js calling conventions.


AWS Lambda has a somewhat unintuitive API structure that is sometimes inconsistent with node.js standards. This library bridges the gap, allowing you to write more familiar node.js style code.


Wrapping your function standardizes the calling conventions across all versions of Node.js and all AWS Lambda event sources. This includes:

  • Supporting Promise returns, rather than the callback argument
  • Standardizing arguments to (event, callback)
  • Providing additional helpers through the this object


var shim = require('@ffleet/shim');
var myLib = require('./lib');

// callback is not needed with Promise
function myHandler(event) {
	// myLib.handle returns a promise
	return myLib.handle(event);

exports.myHandler = shim.wrap(myHandler);


The specific API shims below provide context specific APIs for certain Lambda events.


Node.js HTTP servers are built around request and response objects passing through route handlers. This has been embraced by the common node.js HTTP libraries as well (Express, Hapi, Restify, etc.).

The http shim creates a native node.js HTTP server and proxies the AWS Lambda event.

For example, using a native handler:

const shim = require('@ffleet/shim');

function myNativeHttpHandler(req, res) {
	res.end('Hello, World!');

exports.myNativeHttpHandler = shim.http(myNativeHttpHandler);

Or, you can wrap an entire Express server:

const shim = require('@ffleet/shim');
const express = require('express');
const app = express();

app.get('/', function(req, res, next) {
	res.send('Hello, World!');

exports.myExpressHttpHandler = shim.http(app);


Cron functions are executed by AWS CloudWatch Events. Wrapping with the cron shim unpacks the event data and provides a Date object of when the cron event was generated.

const shim = require('@ffleet/shim');

function myCron(date, callback) {
	console.log('cron event generated at ' + date.toISOString());
exports.myCron = shim.cron(myCron);


AWS CloudWatch Log data is provided in a base64 encoded and gzip packed data string. The logs shim will decode the log data and reconstitute the represented JSON object, as:

	"messageType": "DATA_MESSAGE",
	"owner": "123456789123",
	"logGroup": "testLogGroup",
	"logStream": "testLogStream",
	"subscriptionFilters": ["testFilter"],
	"logEvents": [{
		"id": "eventId1",
		"timestamp": 1440442987000,
		"message": "[ERROR] First test message"
	}, {
		"id": "eventId2",
		"timestamp": 1440442987001,
		"message": "[ERROR] Second test message"


const shim = require('@ffleet/shim');

function myLogHandler(logObject, callback) {
	logObject.logEvents.forEach(logEvent => console.log('log', logEvent));
exports.myLogHandler = shim.logs(myLogHandler);