How to Use TypeScript for AWS Lambda in 3 Steps
AWS Lambda/NodeJS (TypeScript) Series
- How to Use TypeScript for AWS Lambda in 3 Steps
- Unit Test and Integration Test for AWS Lambda/NodeJS in TypeScript
Situation
When we are using NodeJS as the runtime for AWS Lambdas, JavaScript is the default language. However, due to the lack of typing checking in JavaScript, from time to time, buggy code is deployed to Lambda inadvertently. Such as a small typo like this:
exports.lambdaHandler = async (event, context) => {
const queries = event.queytStringParameters;
// ...
}
We mean to get queryStringParameters
, but the queries
ends up undefined
as a result of carelessness.
Goal
We want to utilize TypeScript to write lambda handlers. With TypeScript, we will have the following benefits:
- Vanilla code completion hints while programming
- Compilation time error checks to avoid redundant deployments
It is not hard to do so, this article will introduce 3 steps to complete that job.
Preparation
Before going through the 3 steps, let’s create a classic lambda project with SAM CLI:
sam init
After the above command, we will get a folder with these files:
├── README.md
├── events
│ └── event.json
├── hello-world
│ ├── app.js
│ ├── package.json
│ └── tests
│ └── unit
│ └── test-handler.js
└── template.yaml
Then we will start to shift this JS package into a TS package.
Step 1: Add TypeScript Dependency
In the package.json
, add the following codes:
"scripts": {
"compile": "tsc"
},
"devDependencies": {
"aws-sdk": "^2.655.0",
"@types/aws-lambda": "^8.10.51",
"@types/node": "^13.13.5",
"typescript": "^3.8.3"
}
- scripts/compile: this will be used to compile the TypeScript code to JavaScript
- devDependencies: since this is only for development, we do not need to add the packages to the
dependencies
block - aws-sdk: depending on whether you are using AWS SDK in your lambda
- @types/aws-lambda: this is very vital for the code completion and typing checks
- @types/node: we need this package for built-in types
- typescript: where the
tsc
is from
If you find this article useful, please follow this account for future updates. Thanks for the support!
Step 2: Add tsconfig.json
{
"compilerOptions": {
"module": "CommonJS",
"target": "ES2017",
"noImplicitAny": true,
"preserveConstEnums": true,
"outDir": "./built",
"sourceMap": true
},
"include": ["src-ts/**/*"],
"exclude": ["node_modules", "**/*.spec.ts"]
}
TypeScript compiler needs tsconfig.json
to figure out how to transform TypeScript to JavaScript.
- module: CommonJS is fine here
- target: applying ES2017 will keep the
async
andawait
syntax instead of transforming them toPromise
code. Since we are using Node12 as the runtime environment, Lambda function supports interpreting the syntax. Meanwhile, keepingasync
andawait
makes code clean and short - noImplicitAny: recommended to have. Compiler will throw an error if there is a variable declared without type
- preserveConstEnums: more like a syntax sugar, but I would like to keep it on because it could keep
enum
classes in the JavaScript code in the form ofobject
, which helps understand the JavaScript code - outDir: any folder you would like to set as the compilation output
- sourceMap: this one is optional
Step 3: Change the code
First, create the folder src-ts
, and move app.js
to that folder.
The app.js
looks like this now:
exports.lambdaHandler = async (event, context) => {
const queries = JSON.stringify(event.queytStringParameters);
return {
statusCode: 200,
body: `Queries: ${queries}`
}
};
Let’s create app.ts
and replace it:
import {
APIGatewayProxyEvent,
APIGatewayProxyResult
} from "aws-lambda";export const lambdaHandler = async (
event: APIGatewayProxyEvent
): Promise<APIGatewayProxyResult> => {
const queries = JSON.stringify(event.queryStringParameters);
return {
statusCode: 200,
body: `Queries: ${queries}`
}
}
Since this TypeScript file will be compiled to built
folder, we also need to modify the Handler
field in template.yaml
, to ensure the lambda
resource could locate the code in the right path:
Resources:
HelloWorldFunction:
Type: AWS::Serverless::Function
Properties:
CodeUri: hello-world/built
Handler: app.lambdaHandler
We append the path built
by the folder hello-world
, so that AWS Lambda could find the handler correctly.
Now the directory looks like below:
├── README.md
├── hello-world
│ ├── built
│ │ ├── app.js
│ │ └── app.js.map
│ ├── package-lock.json
│ ├── package.json
│ ├── src-ts
│ │ ├── app.ts
│ │ └── tests
│ └── tsconfig.json
├── samconfig.toml
└── template.yaml
Deploy and Test
cd hello-world
npm install
npm run compile
cd ..
sam deploy --guided
After deployed successfully, we will see the Lambda function in AWS Console as follows:
And we should be able to test the Lambda function using the following command:
▶ curl https://[API_ID].amazonaws.com/Prod/hello\?weather\=sunny
Queries: {"weather":"sunny"}
Conclusion and Next Step
The sample code can be found at: https://github.com/zijing07/aws-lambda-nodejs-ts
I find it really refreshing after utilizing TypeScript support for my Lambda functions. On one hand, it could save me tons of time looking up the API Doc for a method name or the parameter list. On the other hand, tsc
also helps me to detect any potential problems before deploying.
In the next article, I will talk about how to do local integration tests on Lambda functions.
If you find this article useful, please follow this account for future updates. Thanks for the support!
Level Up Coding
Thanks for being a part of our community! Level Up is transforming tech recruiting. Find your perfect job at the best companies.