如何在 typescript 中导出函数

Question

Total Typescript newbie. I'm working on a cdk project. I have a class (stack) that is getting massive. So I want to offload a bunch of methods into other files to keep it manageable.

This works:

import * as cdk from '@aws-cdk/core';
import * as lambda        from '@aws-cdk/aws-lambda';                // need for Runtime
import * as lambda_nodejs from '@aws-cdk/aws-lambda-nodejs';

const TAG = "sn-v1-";

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

      // Lambda: Get stuff from Sigfox API
      // ---------------------------------
      
      const testLambda = new lambda_nodejs.NodejsFunction(this, 'sigfox-get', {
        runtime: lambda.Runtime.NODEJS_12_X,
        entry: 'lambda/sn-prod/sigfox-get.js',
        handler: 'handler',
        functionName: TAG + 'sigfox-get',
        description: 'Get all devices from Sigfox API.',
        memorySize: 256,
        timeout: cdk.Duration.seconds(360)
      });
    }
}

But I want to do something like this:

// class file
import * as cdk from '@aws-cdk/core';
import * as lambda        from '@aws-cdk/aws-lambda';                // need for Runtime
import * as lambda_nodejs from '@aws-cdk/aws-lambda-nodejs';

import { genSigfoxGetLambda } from './sn-prod/api-gw';

export class SnProdStack extends cdk.Stack {
    constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
      super(scope, id, props);      
      const testLambda = this.genSigfoxGetLambda;
    }
}



// method file
import { SnProdStack } from '../sn-prod-stack';

import * as cdk from '@aws-cdk/core';
import * as lambda        from '@aws-cdk/aws-lambda';                // need for Runtime
import * as lambda_nodejs from '@aws-cdk/aws-lambda-nodejs';

const TAG = "sn-v1-";

export function genSigfoxGetLambda(this: SnProdStack) {
    const testLambda = new lambda_nodejs.NodejsFunction(this, 'sigfox-get', {
        runtime: lambda.Runtime.NODEJS_12_X,
        entry: 'lambda/sn-prod/sigfox-get.js',
        handler: 'handler',
        functionName: TAG + 'sigfox-get',
        description: 'Get all devices from Sigfox API.',
        memorySize: 256,
        timeout: cdk.Duration.seconds(360)
      });
      return testLambda;
}

This is a tiny minimal reproducible example. The whole code is enormous, with 10 or 20 of each thing. My plan is to use factory methods for each type of tying I need to make and pass in an options object. Right now, the problem is that the code I've written does nothing at all.

Answer 1

To export a function, we need to add the export directive and to make it available to other files outside of its current folder.

You are already using the export keyword, so now all you need to do is place an index.ts file in every folder.

For example, if we have this directory structure...

.
├── main.ts
└── module
    ├── a.ts
    └── index.ts

...and we wish to export a function from a.ts and use it in main.ts , then the function must use the export keyword and index.ts must export it from module/ .

// a.ts
export const foo = () => { return 'bar'; };

// index.ts
export * from './a';

Then, we may import the function.

// main.ts
import { foo } from './module';

Answer 2

Try something like this from your main stack

import cdk = require("@aws-cdk/core");
import { MyFirstStack } from "../lib/my-first-stack";
import { StepFunctionStack } from "../lib/step-function-stack";

const app = new cdk.App();
const myFirstStack = new MyFirstStack(app, "stackName");
const stepFunctionStack = new StepFunctionStack(app, "stepFunctionStackName");

// If you need to add a dependency on one of your stacks
myFirstStack.addDependency(stepFunctionStack);

Then you can have the other stacks in the location imported from above, in my example its back 1 folder and in a lib folder..

Here is something what one of them stacks would look like

import { Construct, Stack, StackProps } from "@aws-cdk/core";

export class MyFirstStack extends Stack {
  constructor(scope: App, id: string, props?: StackProps) {
    const properties: StackProps = {
      env: {
        region: "us-east-1",
        account: <account>,
      },
    };

    super(scope, id, properties);

    const lambda = create_lambda()

    create_lambda(){
    // code to create lambda etc. 
}