Node.js Beginner Guide

$ node --version
v22.21.1

$ npm --version
10.9.4

$ node -e 'console.log(process.version, process.platform, process.arch)'
v22.21.1 darwin arm64

$ mkdir taskkit && cd taskkit && npm init -y
Wrote to ~/taskkit/package.json:

{
  "name": "taskkit",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

$ node hello.js
Hello from Node v22.21.1
platform: darwin arm64
this file: hello.js
typeof window: undefined

$ node argv.js Mya 3
[
  '~/.nvm/versions/node/v22.21.1/bin/node',
  '~/taskkit/argv.js',
  'Mya',
  '3'
]

The first two items are the node program and the script, so your own arguments start at process.argv[2]. That's why the code below uses slice(2).สองตัวแรกคือโปรแกรม node และสคริปต์ อาร์กิวเมนต์ของเราจึงเริ่มที่ process.argv[2] โค้ดด้านล่างจึงใช้ slice(2)

$ node greet.js
Hello, world!

$ node greet.js Mya 3
Hello, Mya!
Hello, Mya!
Hello, Mya!

$ node greet.js Mya three; echo "exit code: $?"
times must be a whole number above 0, got "three"
exit code: 1

$ GREETING=Sawasdee node -e 'console.log(process.env.GREETING ?? "(not set)")'
Sawasdee

$ node -e 'console.log(process.env.GREETING ?? "(not set)")'
(not set)

$ node notes.js list

$ node notes.js add Learn Node
added #1

$ node notes.js add Read a file
added #2

$ node notes.js done 1
done #1

$ node notes.js list
[x] 1. Learn Node
[ ] 2. Read a file

$ cat notes.json
[
  {
    "id": 1,
    "title": "Learn Node",
    "done": true
  },
  {
    "id": 2,
    "title": "Read a file",
    "done": false
  }
]

$ node notes.js add "   "; echo "exit code: $?"
error: a note needs some text
exit code: 1

$ node notes.js done 9; echo "exit code: $?"
error: no note with id 9
exit code: 1

The first list prints nothing: notes.json didn't exist yet, and loadNotes turns that ENOENT error into an empty list. Errors set process.exitCode = 1 instead of exiting at once, so the program still finishes cleanly.list ครั้งแรกไม่พิมพ์อะไรเลย เพราะยังไม่มี notes.json และ loadNotes เปลี่ยน error ENOENT ให้เป็นรายการว่าง เมื่อเกิดข้อผิดพลาด โค้ดตั้ง process.exitCode = 1 แทนการออกทันที โปรแกรมจึงยังจบได้อย่างเรียบร้อย

$ npm install picocolors

added 1 package, and audited 2 packages in 627ms

found 0 vulnerabilities

$ npm ls
taskkit@1.0.0 ~/taskkit
`-- picocolors@1.1.1

$ npm run notes -- list
> taskkit@1.0.0 notes
> node notes.js list

[x] 1. Learn Node
[ ] 2. Read a file

$ npm run notes -- done 7
> taskkit@1.0.0 notes
> node notes.js done 7

error: no note with id 7

$ node events.js
cook: making pad thai
cashier: billing pad thai
cook: making som tam
cashier: billing som tam
kitchen closed
listeners for order: 2

$ node make-log.js
wrote access.log

$ wc -l access.log
  200000 access.log

$ head -3 access.log
10.0.0.0 GET /page/0 200
10.0.0.1 GET /page/1 200
10.0.0.2 GET /page/2 301

$ node count-errors.js
{ '404': 28571, '500': 28571, total: 200000 }

$ node gzip.js
access.log: 5345 KB → access.log.gz: 634 KB

Notice the key order: '404' and '500' come before total. JavaScript always puts number-like keys first, in numeric order.สังเกตลำดับคีย์: '404' และ '500' มาก่อน total เพราะ JavaScript เรียงคีย์ที่เป็นตัวเลขไว้ก่อนเสมอตามลำดับตัวเลข

$ PORT=5050 node server.js
listening on http://localhost:5050

$ curl -s localhost:5050/notes
[{"id":1,"title":"Learn Node","done":true},{"id":2,"title":"Read a file","done":false}]

$ curl -si -X POST localhost:5050/notes -d '{"text":"Serve JSON"}'
HTTP/1.1 201 Created
Content-Type: application/json
Transfer-Encoding: chunked

{"id":3,"title":"Serve JSON","done":false}

$ curl -s -w "\n%{http_code}\n" -X POST localhost:5050/notes -d '{"text":"   "}'
{"error":"a note needs some text"}
400

$ curl -s -w "\n%{http_code}\n" -X POST localhost:5050/notes -d '{"text":'
{"error":"Unexpected end of JSON input"}
400

$ curl -s -X PATCH localhost:5050/notes/3/done
{"id":3,"title":"Serve JSON","done":true}

$ curl -s -w "\n%{http_code}\n" -X PATCH localhost:5050/notes/99/done
{"error":"no note with id 99"}
404

$ curl -s -w "\n%{http_code}\n" localhost:5050/nope
{"error":"not found"}
404

The server read the two notes the CLI saved in lesson 3. Date and connection headers are left out of the -i output. I ran it on port 5050 because 3000 was already in use on my machine; lesson 12 shows what that error looks like.เซิร์ฟเวอร์อ่านโน้ตสองรายการที่ CLI บันทึกไว้ในบทที่ 3 ส่วนหัววันที่และการเชื่อมต่อถูกตัดออกจากผลลัพธ์ของ -i ผมรันบนพอร์ต 5050 เพราะพอร์ต 3000 ถูกใช้อยู่บนเครื่อง บทที่ 12 แสดงว่าข้อผิดพลาดนั้นหน้าตาเป็นอย่างไร

$ npm install express

added 68 packages, and audited 70 packages in 1s

28 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities

$ PORT=5050 node server.js
listening on http://localhost:5050
GET /notes
POST /notes
PATCH /notes/99/done
GET /nope

$ curl -s localhost:5050/notes
[{"id":1,"title":"Learn Node","done":true},{"id":2,"title":"Read a file","done":false},{"id":3,"title":"Serve JSON","done":true}]

$ curl -s -w "\n%{http_code}\n" -X POST localhost:5050/notes -H "Content-Type: application/json" -d '{"text":"Use Express"}'
{"id":4,"title":"Use Express","done":false}
201

$ curl -s -w "\n%{http_code}\n" -X POST localhost:5050/notes -H "Content-Type: application/json" -d '{"text":'
{"error":"Unexpected end of JSON input"}
400

$ curl -s -w "\n%{http_code}\n" -X PATCH localhost:5050/notes/99/done
{"error":"no note with id 99"}
404

$ curl -s -w "\n%{http_code}\n" localhost:5050/nope
{"error":"not found"}
404

Look at the server's log in terminal 1: there are five requests but only four lines. The one with broken JSON never reached the logger, because express.json() runs first and sent it straight to the error handler. Middleware order matters.ดู log ของเซิร์ฟเวอร์ในเทอร์มินัล 1: มีห้าคำขอแต่มีแค่สี่บรรทัด คำขอที่ JSON เสียไม่ถึงตัว logger เลย เพราะ express.json() ทำงานก่อนและส่งต่อไปที่ตัวจัดการ error ทันที ลำดับของ middleware จึงสำคัญ

$ npm test
> taskkit@1.0.0 test
> node --test --test-reporter=spec

✔ POST /notes creates a note (21.156875ms)
✔ a blank note is rejected with 400 (2.125042ms)
✔ unknown routes return JSON 404 (1.33125ms)
✔ addNote gives the first note id 1 (0.73825ms)
✖ addNote keeps ids growing after a gap (0.35975ms)
✔ addNote rejects blank text (0.441917ms)
✔ markDone throws NotFoundError for a missing id (0.109625ms)
ℹ tests 7
ℹ suites 0
ℹ pass 6
ℹ fail 1
ℹ cancelled 0
ℹ skipped 0
ℹ todo 0
ℹ duration_ms 123.094792

✖ failing tests:

test at test/store.test.js:9:1
✖ addNote keeps ids growing after a gap (0.35975ms)
  AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
  
  3 !== 6
  
      at TestContext.<anonymous> (file://~/taskkit/test/store.test.js:14:10)
      at Test.runInAsyncScope (node:async_hooks:214:14)
      at Test.run (node:internal/test_runner/test:1047:25)
      at Test.processPendingSubtests (node:internal/test_runner/test:744:18)
      at Test.postRun (node:internal/test_runner/test:1173:19)
      at Test.run (node:internal/test_runner/test:1101:12)
      at async startSubtestAfterBootstrap (node:internal/test_runner/harness:296:3) {
    generatedMessage: true,
    code: 'ERR_ASSERTION',
    actual: 3,
    expected: 6,
    operator: 'strictEqual',
    diff: 'simple'
  }

$ npm test
> taskkit@1.0.0 test
> node --test --test-reporter=spec

✔ POST /notes creates a note (19.798583ms)
✔ a blank note is rejected with 400 (3.152875ms)
✔ unknown routes return JSON 404 (1.073167ms)
✔ addNote gives the first note id 1 (0.485042ms)
✔ addNote keeps ids growing after a gap (0.0575ms)
✔ addNote rejects blank text (0.134666ms)
✔ markDone throws NotFoundError for a missing id (0.319125ms)
ℹ tests 7
ℹ suites 0
ℹ pass 7
ℹ fail 0
ℹ cancelled 0
ℹ skipped 0
ℹ todo 0
ℹ duration_ms 100.648416

npm test runs node --test --test-reporter=spec, as set in package.json. It finds every *.test.js file by itself.npm test จะรัน node --test --test-reporter=spec ตามที่ตั้งไว้ใน package.json และหาไฟล์ *.test.js ทุกไฟล์ให้เอง

$ cp .env.example .env

$ node --env-file=.env server.js
listening on http://localhost:5050
GET /notes

$ node --env-file=missing.env server.js; echo "exit code: $?"
node: missing.env: not found
exit code: 9

The first server logged GET /notes because I called it once with curl to check it was up.เซิร์ฟเวอร์ตัวแรกพิมพ์ GET /notes เพราะผมเรียกด้วย curl หนึ่งครั้งเพื่อตรวจว่ามันทำงานอยู่