When we create a new Lambda function written in TypeScript, we have to add any third party extension or configure any build config by myself using like a Webpack, parcel, or babel.

But now, AWS CDK provides a useful official package for TypeScript.

Steps of creating Lambda Function

1: Setup project

$ mkdir ts-api
$ cd ts-api
$ npx aws-cdk init app --language typescript

2: Add AWS CDK Construct library

$ yarn add @aws-cdk/aws-lambda-nodejs
$ yarn add -D @types/aws-lambda

3: Create a Lambda function code

$ vim lambda/entry.ts
import {
    APIGatewayProxyHandler
} from 'aws-lambda'

export const handler: APIGatewayProxyHandler = async (event) => {
    console.log(event)
    return {
        statusCode: 200,
        body: JSON.stringify(event)
    }
}

4: Define AWS resource

$ vim lib/ts-api-stack.ts
import * as cdk from '@aws-cdk/core';
import { NodejsFunction } from '@aws-cdk/aws-lambda-nodejs'

export class DeployToS3Stack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const lambdaFunction = new NodejsFunction(this, 'LambdaFunction', {
      entry: 'lambda/entry.ts',
      handler: 'handler',
    })
  }
}

5: deploy

$ yarn build
$ yarn cdk bootstrap
$ yarn cdk deploy

Add a new REST API endpoint (Lambda proxy)

And we can easy to integrate to AWS API Gateway

1: Install a construct library

$ yarn add @aws-cdk/aws-apigateway

2: Define AWS resource

import * as cdk from '@aws-cdk/core';
import { LambdaRestApi } from '@aws-cdk/aws-apigateway';
import { NodejsFunction } from '@aws-cdk/aws-lambda-nodejs'

export class DeployToS3Stack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const lambdaFunction = new NodejsFunction(this, 'Function', {
      entry: 'lambda/entry.ts',
      handler: 'handler'
    })

    const api = new LambdaRestApi(this, 'API', {
      handler: lambdaFunction,
      proxy: true,
    })
  }
}