Using fp-ts for Functional Programming in TypeScript/

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Creating the Retrieve Lambda

Creating the Retrieve Lambda

Retrieve information about a reservation.

We'll cover the following...

Overview

Next, we’ll retrieve information about a reservation. To do that, we’ll probably have to pass in two bits of information into the Lambda, namely the userId and hotelId. But that might return multiple results if a user has stayed in the hotel before. So, we’ll also pass in the start date of the stay. Because we’re retrieving information but not actually changing anything, the correct HTTP method is GET.

Setup

Create a new directory called retrieve under the Lambdas directory. Copy the webpack config, jest config, and tsconfig from the other Lambda. Those remain the same. The package.json is very similar:

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{
  "name": "leanpub-reservations-retrieve-reservation",
  "version": "1.0.0",
  "description": "Lambda for retrieving a reservation",
  "scripts": {
    "clean": "rm -rf node_modules && rm -rf dist",
    "webpack": "webpack",
    "zip": "cd dist && zip -r retrieve.zip *",
    "build": "npm i && webpack && npm run zip",
    "test": "jest --coverage"
  },
  "dependencies": {
    "fp-ts": "^2.8.3",
    "fp-ts-std": "^0.7.0"
  },
  "devDependencies": {
    "@types/jest": "^26.0.14"
  },
  "author": "Sam Van Overmeire",
  "license": "ISC"
}

There are ways to avoid (most of) this duplication. We can create a single webpack in the project’s root that conducts multiple builds. The tsconfig files can inherit config from a base config and we could do something similar for jest. That said, because we only have two Lambdas, we’ll leave everything as is, including this bit of duplication.

Writing index test in src folder

We again create a src folder with an index file. This time, we’ll start by writing an index test in the __tests__ directory, which only turns green when we’ve completed all our work for this Lambda:

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import {handler} from "../src";
describe('retrieve index test', () => {
    it('should return the asked-for reservation', async () => {
        const startDate = new Date(2020, 11, 10, 12, 0, 0);
        const queryStringParameters = {
            hotelId: '1',
            userId: '11',
            start: startDate.toISOString(),
        }
        const event = {
            queryStringParameters,
        }
        const result: any = await handler(event);
        expect(result.statusCode).toBe(200);
        const body = JSON.parse(result.body);
        expect(body.price).toBe(20);
    });
});

Adding handler function

Now, add an index.ts with handler under the src folder to make it compile:

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import {LambdaEvent} from "../../../util/domain/types";
export const handler = async (event: LambdaEvent) => {
    return {
        statusCode: 200,
    }
};

The ...