how to provision a node service from scratch

We're performing interactive steps adding small things one at a time!

requirements

node 18

minimal hello

mkdir simple-roadmap # create a folder
cd simple-roadmap
npm init -y # creates the `package.json` file, this folder is a node project now
npm i koa
touch index.mjs # you can use just .js extension, but adpting explicit .mjs or .cjs gives more control over module style

This is the initial content of index.mjs:

import Koa from "koa"

const app = new Koa()

app.use(async ctx => ctx.body = "ONLINE")

app.listen(3000)
console.log("http://localhost:3000")

Then add the start script into package.json:

//...
"scripts" {
  "test": "echo \"Error: no test specified\" && exit 1",
  "start": "node index.mjs"
}
//...

And run wih npm start.

adding routes

Koa is highly modular and there is a dedicated plugin to porper manage routes on it.

Install koa-router:

npm i @koa/router

Modify index.mjs:

import Koa from "koa"
import Router from "@koa/router"

const app = new Koa()
const router = new Router()

router.get("/status", async ctx => ctx.body = "ONLINE")

app.use(router.routes()).use(router.allowedMethods())

app.listen(3000)
console.log("http://localhost:3000")

Kill previous npm start and re-run it to see new http://localhost:3000/status endpoint

adding simple database for a todo list

Install level
Install bodyparser

npm i level
npm i @koa/bodyparser

Modify your index.mjs again:

import Koa from "koa"
import Router from "@koa/router"
import { bodyParser } from "@koa/bodyparser"
import { Level } from "level"

const app = new Koa()
const router = new Router()
const db = new Level("sample", { valueEncoding: "json" })

router.get("/status", async ctx => ctx.body = "ONLINE")

router.get("/todos", async ctx =>
  ctx.body = await db.values({ limit: 100 }).all())

router.post("/todos", async ctx => {
  const { message, done } = ctx.request.body
  const key = new Date().getTime()
  const todo = { key, message, done }
  await db.put(key, todo)
  ctx.body = todo
})

app.use(bodyParser())
app.use(router.routes()).use(router.allowedMethods())

app.listen(3000)
console.log("http://localhost:3000")

Kill previous console again and re-run. Then open a second console and save your first todo:

curl -X POST http://localhost:3000/todos -H 'Content-Type: application/json' -d '{"message":"hello"}'

Check if it was properly saved visiting http://localhost:3000/todos

add nodemon for better DX

Install nodemon so you don't need to kill and restart every time:

npm i -D nodemon

Then modify the scripts section on package.json:

//...
"scripts" {
  "test": "echo \"Error: no test specified\" && exit 1",
  "start": "node index.mjs",
  "dev": "nodemon index.mjs"
}
//...

For now on, start the program with npm run dev

time to proper modularize the script

After add a few more endpoints to complete the REST service, that script will become too horrible to watch:

import Koa from "koa"
import Router from "@koa/router"
import { bodyParser } from "@koa/bodyparser"
import { Level } from "level"

const app = new Koa()
const router = new Router()
const db = new Level("sample", { valueEncoding: "json" })

router.get("/status", async ctx => ctx.body = "ONLINE")

router.get("/todos", async ctx =>
  ctx.body = await db.values({ limit: 100 }).all())

router.get("/todos/:key", async ctx =>
  ctx.body = await db.get(ctx.params.key))

router.post("/todos", async ctx => {
  const { message, done } = ctx.request.body
  const key = new Date().getTime()
  const todo = { key, message, done }
  await db.put(key, todo)
  ctx.body = todo
})

router.put("/todos/:key", async ctx => {
  const { message, done } = ctx.request.body
  const key = ctx.params.key
  const todo = { key, message, done }
  await db.put(key, todo)
  ctx.body = todo
})

router.del("/todos/:key", async ctx =>
  ctx.body = await db.del(ctx.params.key))

app.use(bodyParser())
app.use(router.routes()).use(router.allowedMethods())

app.listen(3000)
console.log("http://localhost:3000")

Strictly speaking it works, but it's very coupled and troublesome to test except for integration tests.

Little opportunity for modularization.

Let's start by creating a folder structure and some boilerplate:

mkdir -p app/{controller,service,config}
touch app/controller/todoRequests.mjs app/service/todoService.mjs app/config/db.mjs app/main.mjs

We'll dismantle our single file project into this opinionated folder structure so we can put each concern in it's own place.

Why app folder instead of src folder

Use src whenever you have any compilation step for your code -- typescript for example.

Use app folder if it is meant to run the way it is.

app/config/db.mjs

import { Level } from "level"

export const db = new Level("sample", { valueEncoding: "json" })

app/service/todoService.mjs

import { db } from "../config/db.mjs"

export const listTodoService = async () =>
  await db.values({ limit: 100 }).all()

export const findTodoService = async key =>
  await db.get(key)

export const insertTodoService = async ({ message, done }) =>
  await updateTodoService({ key: new Date().getTime(), message, done })

export const updateTodoService = async ({ key, message, done }) => {
  const todo = { key, message, done }
  await db.put(key, todo)
  return todo
}

export const delTodoService = async key =>
  await db.del(key)

app/controller/todoRequests.mjs

import { 
  delTodoService, 
  findTodoService, 
  insertTodoService, 
  listTodoService, 
  updateTodoService 
} from "../service/todoService.mjs"

export const listTodoRequest = async ctx => {
  ctx.body = await listTodoService()
}

export const findTodoRequest = async ctx => {
  const { key } = ctx.params
  ctx.body = await findTodoService(key)
}

export const insertTodoRequest = async ctx => {
  const { message, done } = ctx.request.body
  ctx.body = await insertTodoService({ message, done })
}

export const updateTodoRequest = async ctx => {
  const { message, done } = ctx.request.body
  const { key } = ctx.params
  ctx.body = await updateTodoService({ key, message, done })
}

export const delTodoRequest = async ctx => {
  const { key } = ctx.params
  ctx.body = await delTodoService(key)
}

app/main.mjs

import Koa from "koa"
import Router from "@koa/router"
import { bodyParser } from "@koa/bodyparser"
import {
  delTodoRequest,
  findTodoRequest,
  insertTodoRequest,
  listTodoRequest,
  updateTodoRequest
} from "./controller/todoRequests.mjs"

export const app = new Koa()
const router = new Router()

router.get("/status", async ctx => ctx.body = "ONLINE")

router.get("/todos", listTodoRequest)
router.get("/todos/:key", findTodoRequest)
router.post("/todo", insertTodoRequest)
router.put("/todo/:key", updateTodoRequest)
router.del("/todo/:key", delTodoRequest)

app.use(bodyParser())
app.use(router.routes()).use(router.allowedMethods())

index.mjs

Finally we rewrite the index.mjs once again:

import { app } from "./app/main.mjs"

app.listen(3000)
console.log("http://localhost:3000")

No need to restart the service, nodemon did that for us.

We now have what people call separation of concerns.

Adding some tests

Install mocha
Install chai

npm i -D mocha chai

Create a test spec (app/service/todoService.spec.mjs):

import * as service from "./todoService.mjs"

import chai, {expect} from "chai"

chai.should()

describe("simple unit test suite", () => {

  const message = `message ${new Date().getTime()}`
  const messageUpdated = `message ${new Date().getTime()} updated`

  let key = -1

  it("should create a todo", async () => {
    const result = await service.insertTodoService({ message })
    result.message.should.be.eql(message)
    key = result.key
  })

  it("should list a todo", async () => {
    const result = await service.listTodoService()
    result.should.be.an('Array')
  })

  it("should find a todo", async () => {
    const result = await service.findTodoService(key)
    result.should.be.an('Object')
    result.key.should.be.eql(key)
  })

  it("should update a todo", async () => {
    const result = await service.updateTodoService({ key, messageUpdated })
    result.should.be.an('Object')
    result.key.should.be.eql(key)
  })

  it("should delete a todo", async () => {
    const result = await service.delTodoService(key)
    expect(result).to.be.undefined
  })
})

Then modify your test script on package.json:

//...
"scripts" {
  "test": "mocha --recursive app",
  "start": "node index.mjs",
  "dev": "nodemon index.mjs"
}
//...

Call the tests either with npm run test or with npx mocha --recursive app.

Tests are good because having them passing means that the code is supposed to be doing what it should do.

Adding coverage

Install c8

npm i -D c8

Then add a test:coverage script on package.json:

//...
"scripts" {
  "test": "mocha --recursive app",
  "test:coverage": "c8 npm run test",
  "start": "node index.mjs",
  "dev": "nodemon index.mjs"
}
//...

And run it:

npm run test:coverage

This is the sample output:

> simple-roadmap@1.0.0 test:coverage
> c8 npm run test


> simple-roadmap@1.0.0 test
> mocha --recursive app



  simple unit test suite
    ✔ should create a todo
    ✔ should list a todo
    ✔ should find a todo
    ✔ should update a todo
    ✔ should delete a todo


  5 passing (8ms)

-----------------------|---------|----------|---------|---------|-------------------------------
File                   | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s             
-----------------------|---------|----------|---------|---------|-------------------------------
All files              |   87.39 |      100 |      50 |   87.39 |                               
 app                   |     100 |      100 |     100 |     100 |                               
  main.mjs             |     100 |      100 |     100 |     100 |                               
 app/config            |     100 |      100 |     100 |     100 |                               
  db.mjs               |     100 |      100 |     100 |     100 |                               
 app/controller        |   53.12 |      100 |       0 |   53.12 |                               
  todoRequests.mjs     |   53.12 |      100 |       0 |   53.12 | 10-11,14-16,19-21,24-27,30-32 
 app/service           |     100 |      100 |     100 |     100 |                               
  todoService.mjs      |     100 |      100 |     100 |     100 |                               
  todoService.spec.mjs |     100 |      100 |     100 |     100 |                               
-----------------------|---------|----------|---------|---------|-------------------------------

Process finished with exit code 0

Having tests is good, but it's coverage to explain how much we can trust the tests and the code.

Mock some calls

Install chai-http
Install chai-sinon
Install sinon

npm i -D chai-http sinon-chai sinon

Create a spec file (app/controller/todoRequests.spec.mjs):

import chai, {expect} from "chai"
import chaiHttp from "chai-http"
import sinonChai from "sinon-chai"
import * as sinon from "sinon";

import * as controller from "./todoRequests.mjs"
import {app} from "../main.mjs"
import {db} from "../config/db.mjs"

chai.should()
chai.use(chaiHttp)
chai.use(sinonChai)

describe("simple requests test suite", () => {

  const sandbox = sinon.createSandbox();

  beforeEach(function () {
    sandbox.spy(db);
  });

  afterEach(function () {
    sandbox.restore();
  });

  it("should return 'ONLINE' status", done => {
    chai
      .request(app.callback())
      .get("/status")
      .end((err, res) => {
        res.text.should.be.eql('ONLINE')
        done()
      })
  })

  it("should list todos", (done) => {
    chai
      .request(app.callback())
      .get("/todos")
      .end((err, res) => {
        res.body.should.be.an("Array")
        done()
      })
  })

  it("should insert a todo", async () => {
    const ctx = {request: {body: {message: "hello"}}, body: ""}
    await controller.insertTodoRequest(ctx)
    db.put.should.have.been.calledOnce // sinon-chai in action
  })
})

Here we can see chai-http doing some integration tests, and also we can see sinon spying on db calls.

Make the app aware of the environment

In order to make application more configurable and flexible, we can add checks on environment variables, so we tweak the app behavior accordingly.

We can make listening port configurable:

// index.mjs
import { app } from "./app/main.mjs"

const PORT = process.env.PORT || 3000

app.listen(PORT)
console.log(`http://localhost:${PORT}`)

If PORT environment variable is set, it will be used as listening port.

If no value is set for PORT environment variable, it fallbacks to 3000.

We can make database configurable:

import { Level } from "level"

const LEVELDB = process.env.LEVELDB || "sample"

export const db = new Level(LEVELDB, { valueEncoding: "json" })
console.log(`database is ${LEVELDB}`)

Use .env files

Once the app understands and expects some environment variables it's up to you to properly configure them. Depending on how many projects are present in the developer machine or any other external issue, it might be more tricky than it should be.

On can make use of dot env files to proper manage such variables at development time.

Install dotenv-flow

npm i dotenv-flow

Then create a file called .env and add your environment variables:

# variables needed by the application
PORT=3000
LEVELDB=sample
EXTRA_CONFIG=xpto

Finally, you must make the application aware of those variables. To do so, you need to call the config() function at entry point, but it's invasive; instead, modify start and dev scripts in package.json to perform dynamic loading:

//...
"scripts" {
  "test": "mocha --recursive app",
  "test:coverage": "c8 npm run test",
  "start": "node -r dotenv-flow/config index.mjs",
  "dev": "nodemon -r dotenv-flow/config index.mjs"
}
//...

Check if it is working with this change in index.mjs:

import { app } from "./app/main.mjs"

const PORT = process.env.PORT || 3000

app.listen(PORT)
console.log(`http://localhost:${PORT}`)
console.log(`EXTRA_CONFIG is ${process.env.EXTRA_CONFIG}`)

Kill nodemon process because dynamic loading occurs at startup.

the output should be something like this:

/usr/bin/npm run dev

> simple-roadmap@1.0.0 dev
> nodemon -r dotenv-flow/config index.mjs

[nodemon] 3.0.1
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): *.*
[nodemon] watching extensions: js,mjs,cjs,json
[nodemon] starting `node -r dotenv-flow/config index.mjs`
database is sample
http://localhost:3000
EXTRA_CONFIG is xpto

Name		Name	Last commit message	Last commit date
Latest commit History 4 Commits
app		app
.env		.env
.gitignore		.gitignore
README.md		README.md
index.mjs		index.mjs
package-lock.json		package-lock.json
package.json		package.json

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Repository files navigation

how to provision a node service from scratch

requirements

minimal hello

adding routes

adding simple database for a todo list

add nodemon for better DX

time to proper modularize the script

Why app folder instead of src folder

app/config/db.mjs

app/service/todoService.mjs

app/controller/todoRequests.mjs

app/main.mjs

index.mjs

Adding some tests

Adding coverage

Mock some calls

Make the app aware of the environment

Use .env files

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estacio-alunos/node-simple

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Repository files navigation

how to provision a node service from scratch

requirements

minimal hello

adding routes

adding simple database for a todo list

add nodemon for better DX

time to proper modularize the script

Why app folder instead of src folder

app/config/db.mjs

app/service/todoService.mjs

app/controller/todoRequests.mjs

app/main.mjs

index.mjs

Adding some tests

Adding coverage

Mock some calls

Make the app aware of the environment

Use .env files

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