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Deploy Netlify Functions with TypeScript

atila profile image Atila Fassina ・3 min read

Netlify has recently reached 1 MILLION DEVELOPERS. That’s a lot of happy consumers. To celebrate that, here‘s a step-by-step guide to deploy your very own Netlify Function with TypeScript.

📹 If you prefer, you can have this post as a screencast video.

Please don’t forget to 👍 and 🔔 on your way out if it helped you. It would help me a ton!!! 💕

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.

[build]
  command = "yarn build"
  functions = "lambda"

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

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

{
  "presets": [
    "@babel/preset-typescript",
    [
      "@babel/preset-env",
      {
        "targets": {
          "node": true
        }
      }
    ]
  ]
}
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Create your script tasks

Almost done, run over to your package.json and add the two tasks you’re going to need:

"build": "netlify-lambda build src",
"ts-check": "tsc --noEmit --lib ES2015 ./src/*.ts"
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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 I’d consider a good practice to check your types on CI pipeline, at the very least.

🚨 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 you’re good to go.

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

{ 
  "msg": "BlackLivesMatter"
}
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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.

Deploy

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. 😁

Discussion (9)

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cvuorinen profile image
Carl Vuorinen

Thanks, nice tutorial. That .babelrc with targets node:true made it work (the example given in netlify-lambda README did not work for me without adding that).

Also, the redirect trick was nice, haven't used Netlify redirects before. But I changed it a little bit since I have a project with multiple functions:

[[redirects]]
  from = "/*"
  to = "/.netlify/functions/:splat"
  status = 200
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parkan profile image
Arkadiy Kukarkin

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
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atila profile image
Atila Fassina Author • Edited

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

❯ tsc --version
Version 4.0.3

❯ yarn ts-check
yarn run v1.22.5
$ tsc --noEmit --lib ES2015 ./src/*.ts
✨  Done in 0.77s.

Plus { msg } definitely exists in type [name: string] : string 😜

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parkan profile image
Arkadiy Kukarkin

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)

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parkan profile image
Arkadiy Kukarkin • Edited

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)

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gregorip02 profile image
Gregori Piñeres

Great article, thanks 🤟

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atila profile image
Atila Fassina Author

Thanks a lot, Gregori!

I'm very glad you liked it! 😁

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alexandrudanpop profile image
Alexandru-Dan Pop

Nice tutorial!

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atila profile image
Atila Fassina Author

Thanks a lot, Alexandru!

I'm glad it was useful! 💪