promiser-to-lambda

Construct an AWS Lambda handler from a function that returns a promise.

promiserToLambda(promiser)

Returns an event handler function for use with AWS Lambda. Accepts a single promiser argument, a Lambda handler implemented in promise style. The promiser takes the Lambda event and context as its two arguments, and is expected to return a promise whose resolved value will be passed as the successful result to the Lambda callback. Any error that is thrown within the promise chain will be caught and returned as the error result of the Lambda callback. If function throws an error outside of the promise chain, it will be caught and handled similarly.

Note: Because of the way this wrapper is implemented with the Bluebird library, the promiser function is not technically required to return a Promise. It can return any value that you want to pass to the Lambda handler callback.

Note: This wrapper will also set the context.callbackWaitsForEmptyEventLoop flag to false, preventing Lambda from waiting for the event loop to empty post-callback. This allows Lambda functions to, for instance, maintain frozen database connection pools for quicker responses after cold starts.

Example:

const Promise = require('bluebird');
const promiserToLambda = require('promiser-to-lambda');

const promiser = event => {
	return Promise.resolve(event.message)
		.delay(2000)
		.then(message => {
			console.log('Received:', message);
			let output = message.replace(/o/g, 'x');
			console.log('Returning:', output);
			return output;
		});
}

exports.handler = promiserToLambda(promiser);