With TypeScript

here's an example of how you can write a custom middleware for a Lambda receiving events from API Gateway:

import middy from '@middy/core'
import { APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda'

const middleware = (): middy.MiddlewareObj<APIGatewayProxyEvent, APIGatewayProxyResult> => {
  const before: middy.MiddlewareFn<APIGatewayProxyEvent, APIGatewayProxyResult> = async (
    request
  ): Promise<APIGatewayProxyResult> => {
    // Your middleware logic
  }

  const after: middy.MiddlewareFn<APIGatewayProxyEvent, APIGatewayProxyResult> = async (
    request
  ): Promise<void> => {
    // Your middleware logic
  }

  return {
    before,
    after
  }
}

export default middleware

Note: The Middy core team does not use TypeScript often and we can't certainly claim that we are TypeScript experts. We tried our best to come up with type definitions that should give TypeScript users a good experience. There is certainly room for improvement, so we would be more than happy to receive contributions 😊

See devDependencies for each middleware for list of dependencies that may be required with transpiling TypeScript.