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Deploy Netlify Functions with TypeScript

atila profile image Atila Fassina ใƒป3 min read

Netlify has recently reached 1 MILLION DEVELOPERS. Thatโ€™s a lot of happy consumers. To celebrate that, hereโ€˜s a step-by-step guide to deploy your very own Netlify Function with TypeScript.

๐Ÿ“น If you prefer, you can have this post as a screencast video.

Please donโ€™t forget to ๐Ÿ‘ and ๐Ÿ”” on your way out if it helped you. It would help me a ton!!! ๐Ÿ’•

Also, check the whole source code on github/monster-as-a-service

Configuring netlify.toml

Our first needed step is to configure our Netlify deploy. If you prefer, you can set this up on the dashboard as well, but I find the configuring file more straightforward. To each their own, though.

  command = "yarn build"
  functions = "lambda"

# this is actually a Rewrite
# totally optional, but makes up for
# a much better UX
  from = "/"
  to = "/.netlify/functions/index"
  status = 200

Teaching TypeScript to Babel

Now we need to setup our .babelrc so Babel can use the TypeScript compiler (tsc)

  "presets": [
        "targets": {
          "node": true

Create your script tasks

Almost done, run over to your package.json and add the two tasks youโ€™re going to need:

"build": "netlify-lambda build src",
"ts-check": "tsc --noEmit --lib ES2015 ./src/*.ts"

The only mandatory one is build, but I imagine you will want to be able to check all your types at some point. For any production level TypeScript code Iโ€™d consider a good practice to check your types on CI pipeline, at the very least.

๐Ÿšจ That's because Babel will not check your types, simply run the compiler.

Bare bones function with TypeScript

The only thing you need to have a working Netlify Function is to export a handler method from your .js or .ts file. Netlify Functions run AWS-Lambdas under the hood. So, to have your handler typed, you can simply add types/aws-lambda and youโ€™re good to go.

Hereโ€™s a useful example:

import { APIGatewayEvent, Context } from 'aws-lambda'

export async function handler (
  event: APIGatewayEvent,
  context: Context
) {

  const { msg } = event.queryStringParameters

  return {
    statusCode: 200,
     headers: {
      'Content-Type': 'application/json'
    body: JSON.stringify({ msg })

In that case, if you hit https://your-lambda.netlify.app?msg=BlackLivesMatter if will return the following json:

  "msg": "BlackLivesMatter"

I recommend you to install netlify-dev globally so you can simulate production environment in your machine. If you have the package, you can run netlify dev and it will boot up a server for you and expose your lambda on https://localhost:8888 by default.

If linked to your Netlify Account, the CLI will also allow you to deploy your project without pushing it to anywhere.


Netlify offers you a few ways of deploying your code. The most common is by setting Continuous Deployment by integrating it with your Github, Gitlab, or Bitbucket account.

Another way to do it though, is using Netlify-Dev CLI and hitting netlify deploy.


In case you have found this post useful, please consider sharing it with your network, that would help me a lot to continue sharing posts like this and others. ๐Ÿ˜

Posted on by:

atila profile

Atila Fassina


๐Ÿ’š JAMstack, Design Systems, and tooling


markdown guide

the sample snippet doesn't build for me:

error TS2339: Property 'msg' does not exist on type '{ [name: string]: string; } | null'.

8   const { msg } = event.queryStringParameters

Interesting... it works well for me, code runs as expected and ts-checks return no warnings or errors

โฏ tsc --version
Version 4.0.3

โฏ yarn ts-check
yarn run v1.22.5
$ tsc --noEmit --lib ES2015 ./src/*.ts
โœจ  Done in 0.77s.

Plus { msg } definitely exists in type [name: string] : string ๐Ÿ˜œ


ok, I see the issue, the tsconfig I was inheriting from (node12) sets strict: true, which does not pass in this case

specifically, it seems that this fails because strict implies strictNullChecks, and given that this type is nullable it won't pass (if I cast it as { [name: string] : string } it's ok)


fixed it as follows:

interface EchoQueryParams {
  msg?: String
const { msg } = event.queryStringParameters as EchoQueryParams

(note, this won't actually enforce runtime type checks, but it will make it compile)


Thanks a lot, Alexandru!

I'm glad it was useful! ๐Ÿ’ช


Thanks a lot, Gregori!

I'm very glad you liked it! ๐Ÿ˜