Node AWS Lambda Handler

An AWS Lambda function using the Node.js 22.x runtime should look something like this:

File: index.mjs (original version)

export const handler = async (event, context) => { (1)
  const response = {
    statusCode: 200,
    body: JSON.stringify({
      message: "Hello, World!"
    })
  };
  return response; (2)
};

The handler function has two parameters:

event: This parameter is an object that is used to pass in event data to the handler. It contains, among others, the information detailed in the following table:

Table 1. Contents of Event
Keys	Associated Value
`event.version`	A string with the current version of this event object. Should be `'2.0'` at the time of this writing.
`event.rawPath`	A string with the request path (for example `/some_resource`).
`event.queryStringParameters`	An object with the query string parameters (only if it actually has any).
`event.headers`	An object with the request headers.
`event.body`	A string with the request body (only if it actually has one).
`event.requestContext.domainName`	A string with the domain name of the server where the AWS Lambda function is hosted.
`event.requestContext.http.method`	A string with the request HTTP method (`GET` or `POST`, for example).
`event.requestContext.http.protocol`	A string with the HTTP version used by the request (`HTTP/1.1`, for example).

context: This parameter provides runtime information to your handler. Its type is LambdaContext.

The handler should return an object from which the HTTP response will be constructed.

Table 2. Object Keys for HTTP Response
Key	Description
`statusCode`	An integer number with the HTTP response status code.
`body`	A string with the response body. Typically, the result of calling `JSON.stringify` method to produce JSON output.
`headers`	This is an optional key, but if provided it should refer to an object with additional response headers.