CDK GraphqlApi with Function Using Typescript Causes Undefined or Not Exported - aws-cdk

Question

I have a aws_appsync.GraphqlApi with a lambda resolver:
import * as cdk from 'aws-cdk-lib';
import {aws_appsync} from 'aws-cdk-lib';
import {Construct} from 'constructs';
import {AttributeType, BillingMode, Table} from "aws-cdk-lib/aws-dynamodb";
import * as path from "path";
import {FieldLogLevel} from "aws-cdk-lib/aws-appsync";
import {RetentionDays} from "aws-cdk-lib/aws-logs";
import {Code, Function, Runtime} from "aws-cdk-lib/aws-lambda";
export class RelmStack extends cdk.Stack {
constructor(scope: Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
const relmTable = new Table(this, 'relm', {
billingMode: BillingMode.PAY_PER_REQUEST,
tableName: 'relm',
partitionKey: {
name: 'pk',
type: AttributeType.STRING
}, sortKey: {
name: 'sk',
type: AttributeType.STRING
}
})
const api = new aws_appsync.GraphqlApi(this, 'relm-api', {
name: 'relm-api',
logConfig: {
fieldLogLevel: FieldLogLevel.ALL,
excludeVerboseContent: true,
retention: RetentionDays.TWO_WEEKS
},
schema: aws_appsync.SchemaFile.fromAsset(path.join(__dirname, 'schema.graphql')),
authorizationConfig: {
defaultAuthorization: {
authorizationType: aws_appsync.AuthorizationType.API_KEY,
apiKeyConfig: {
name: 'relm-api-key'
}
}
}
})
const createLambda = new Function(this, 'dialog-create', {
functionName: 'dialog-create',
runtime: Runtime.NODEJS_14_X,
handler: 'index.handler',
code: Code.fromAsset('src/lambda'),
memorySize: 3008,
})
const createDataSource = api.addLambdaDataSource('create-data-source', createLambda)
createDataSource.createResolver('create-resolver', {
typeName: 'Mutation',
fieldName: 'dialogCreate'
});
relmTable.grantWriteData(createLambda);
}
}
The sources lives under src/lambda/index.ts and the code is as follows:
exports.handler = async (event: any) => {
console.log('event: ', event)
};
Super simple. When the file extension is index.js everything works. When I change it to index.ts I get an error:
"index.handler is undefined or not exported"
I've looked at many examples on how to do this and all of them seem to be using the ts extension with no problems. What am I doing wrong here?

Answer 1

You should use the NodejsFunction which includes transpiling TypeScript to JavaScript.
https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_lambda_nodejs-readme.html

Answer 2

You can write your handler in typescript but you'll have to invoke a build script to transpile it into javascript to serve as your lambda handler.
This project uses cdk and tsc:
https://github.com/mavi888/cdk-typescript-lambda/blob/main/package.json
This line discusses using esbuild to transpile:
https://docs.aws.amazon.com/lambda/latest/dg/typescript-package.html