JSON Formatter JavaScript — JSON.stringify()

const serverConfig = {
  host: "api.payments.internal",
  port: 8443,
  workers: 4,
  tls: { enabled: true, cert: "/etc/ssl/certs/api.pem" },
  rateLimit: { requestsPerMinute: 1000, burst: 50 }
}

console.log(JSON.stringify(serverConfig, null, 2))
// {
//   "host": "api.payments.internal",
//   "port": 8443,
//   "workers": 4,
//   "tls": {
//     "enabled": true,
//     "cert": "/etc/ssl/certs/api.pem"
//   },
//   "rateLimit": {
//     "requestsPerMinute": 1000,
//     "burst": 50
//   }
// }

const telemetryEvent = {
  eventId: "evt_3c7f9a2b",
  service: "checkout-api",
  severity: "warn",
  latencyMs: 342,
  region: "eu-west-1",
  tags: ["payment", "timeout", "retry"]
}

// 2-mellanslags indragning (vanligast i JS-projekt)
JSON.stringify(telemetryEvent, null, 2)

// Tabb-indragning (föredras av vissa linters och konfigurationsverktyg)
JSON.stringify(telemetryEvent, null, '\t')

// Kompakt — inga blanktecken (för nätverksöverföring)
JSON.stringify(telemetryEvent)
// {"eventId":"evt_3c7f9a2b","service":"checkout-api",...}

const order = {
  orderId: "ord_8f2a91bc",
  customer: {
    id: "usr_4421",
    email: "e.lindqvist@exempel.se",
    passwordHash: "bcrypt:$2b$12$XKzV..."
  },
  items: [{ sku: "HDMI-4K-2M", qty: 2, unitPrice: 12.99 }],
  createdAt: "2026-03-10T14:22:00Z"
}

// Inkludera bara säkra fält i loggutdata
const safeLog = JSON.stringify(order, ["orderId", "items", "createdAt"], 2)
// {
//   "orderId": "ord_8f2a91bc",
//   "items": [{ "sku": "HDMI-4K-2M", "qty": 2, "unitPrice": 12.99 }],
//   "createdAt": "2026-03-10T14:22:00Z"
// }
// passwordHash och customer.email är exkluderade

const auditRecord = {
  requestId: "req_7d2e91",
  user: { id: "usr_4421", email: "e.lindqvist@exempel.se", apiKey: "sk-live-eKx9..." },
  action: "update_billing",
  timestamp: new Date("2026-03-10T14:22:00Z"),
  durationMs: 87
}

function safeReplacer(key, value) {
  // Redigera fält som ser ut som hemligheter eller personuppgifter
  if (key === "apiKey") return "[REDACTED]"
  if (key === "email") return value.replace(/(?<=.{2}).+(?=@)/, "***")
  return value
}

console.log(JSON.stringify(auditRecord, safeReplacer, 2))
// {
//   "requestId": "req_7d2e91",
//   "user": { "id": "usr_4421", "email": "e.***@exempel.se", "apiKey": "[REDACTED]" },
//   "action": "update_billing",
//   "timestamp": "2026-03-10T14:22:00.000Z",
//   "durationMs": 87
// }

const webhook = {
  eventType: "payment.succeeded",
  occurredAt: new Date("2026-03-10T14:22:00Z"),
  processedAt: new Date()
}

JSON.stringify(webhook, null, 2)
// {
//   "eventType": "payment.succeeded",
//   "occurredAt": "2026-03-10T14:22:00.000Z",
//   "processedAt": "2026-03-10T14:22:01.347Z"
// }

// Alla objekt med en toJSON()-metod behandlas likadant:
const custom = { toJSON: () => "custom-value", hidden: 42 }
JSON.stringify(custom) // '"custom-value"'

class Money {
  constructor(amount, currency) {
    this.amount = amount
    this.currency = currency
  }
  toJSON() {
    // Anropas automatiskt av JSON.stringify
    return { amount: this.amount, currency: this.currency, formatted: `${this.currency} ${this.amount.toFixed(2)}` }
  }
}

class OrderId {
  constructor(id) { this.id = id }
  toJSON() { return this.id }  // Serialisera som enkel sträng
}

const invoice = {
  invoiceId: new OrderId('inv_8f2a91bc'),
  subtotal: new Money(199.00, 'SEK'),
  tax:      new Money(15.92, 'SEK'),
  issuedAt: new Date('2026-03-10T14:22:00Z')
}

JSON.stringify(invoice, null, 2)
// {
//   "invoiceId": "inv_8f2a91bc",
//   "subtotal": { "amount": 199, "currency": "SEK", "formatted": "SEK 199.00" },
//   "tax": { "amount": 15.92, "currency": "SEK", "formatted": "SEK 15.92" },
//   "issuedAt": "2026-03-10T14:22:00.000Z"
// }

// Det här kastar: TypeError: Do not know how to serialize a BigInt
// JSON.stringify({ sessionId: 9007199254741234n })

// Lösning: konvertera BigInt till sträng i replacer
function bigIntReplacer(_key, value) {
  return typeof value === 'bigint' ? value.toString() : value
}

const metrics = {
  requestCount: 9007199254741234n,  // överskrider Number.MAX_SAFE_INTEGER
  service: "ingestion-worker",
  region: "eu-north-1"
}

JSON.stringify(metrics, bigIntReplacer, 2)
// {
//   "requestCount": "9007199254741234",
//   "service": "ingestion-worker",
//   "region": "eu-north-1"
// }

// Det här kastar: TypeError: Converting circular structure to JSON
// const node = { id: "n1" }; node.self = node; JSON.stringify(node)

// Lösning: spåra sedda objekt med ett WeakSet
function circularReplacer() {
  const seen = new WeakSet()
  return function (_key, value) {
    if (typeof value === 'object' && value !== null) {
      if (seen.has(value)) return '[Circular]'
      seen.add(value)
    }
    return value
  }
}

const parent = { id: "node_parent", label: "root" }
const child  = { id: "node_child", parent }
parent.child = child  // cirkulär

JSON.stringify(parent, circularReplacer(), 2)
// {
//   "id": "node_parent",
//   "label": "root",
//   "child": { "id": "node_child", "parent": "[Circular]" }
// }

// Alternativt: npm install flatted
// import { stringify } from 'flatted'
// stringify(parent)  // hanterar cirkulära refs nativt

import { readFileSync, writeFileSync } from 'fs'

try {
  const raw = readFileSync('./config/database.json', 'utf8')
  const config = JSON.parse(raw)
  writeFileSync('./config/database.json', JSON.stringify(config, null, 2))
  console.log('Konfigurationen har formaterats om')
} catch (err) {
  console.error('Misslyckades att formatera om konfigurationen:', err.message)
  // JSON.parse kastar SyntaxError om filen innehåller ogiltig JSON
  // readFileSync kastar ENOENT om filen inte existerar
}

import { readFile, writeFile } from 'fs/promises'

async function reformatJson(filePath) {
  const raw = await readFile(filePath, 'utf8')
  const parsed = JSON.parse(raw)
  const formatted = JSON.stringify(parsed, null, 2)
  await writeFile(filePath, formatted, 'utf8')
  return { keys: Object.keys(parsed).length }
}

// Användning
const { keys } = await reformatJson('./config/feature-flags.json')
console.log(`Formaterade om ${keys} toppnivånycklar`)

// Mönster 1: response.json() → pretty print
async function debugEndpoint(url) {
  const res = await fetch(url, {
    headers: { Authorization: `Bearer ${process.env.API_TOKEN}` }
  })
  if (!res.ok) throw new Error(`HTTP ${res.status}: ${res.statusText}`)

  const data = await res.json()
  console.log(JSON.stringify(data, null, 2))
}

await debugEndpoint('https://api.stripe.com/v1/charges?limit=3')

// Mönster 2: response.text() → parse → format
// Användbart när du vill logga både råsvaret och pretty-printat
async function inspectRawResponse(url) {
  const res = await fetch(url)
  const raw = await res.text()

  console.log('Råsvarets längd:', raw.length)
  try {
    const parsed = JSON.parse(raw)
    console.log('Formaterat:')
    console.log(JSON.stringify(parsed, null, 2))
  } catch {
    console.error('Svaret är inte giltig JSON:', raw.slice(0, 200))
  }
}

# Pretty-printa package.json med node -p (print)
node -p "JSON.stringify(require('./package.json'), null, 2)"

# Pretty-printa från stdin (pipe-vänligt, fungerar i CI)
echo '{"port":3000,"env":"production"}' | node -e "
  const d = require('fs').readFileSync(0, 'utf8')
  console.log(JSON.stringify(JSON.parse(d), null, 2))
"

# Pretty-printa ett sparat API-svar
cat api-response.json | node -e "
  process.stdin.setEncoding('utf8')
  let s = ''
  process.stdin.on('data', c => s += c)
  process.stdin.on('end', () => console.log(JSON.stringify(JSON.parse(s), null, 2)))
"

# Python-fallback (förinstallerat på macOS och de flesta Linux-distributioner)
cat api-response.json | python3 -m json.tool

# jq — snabbast och mest funktionsrikt (brew install jq / apt install jq)
cat api-response.json | jq .

# jq — pretty-printa och filtrera i ett steg
cat api-response.json | jq '.data.users[] | {id, email}'

npm install fast-json-stringify

import fastJson from 'fast-json-stringify'

const serializeTelemetryEvent = fastJson({
  title: 'TelemetryEvent',
  type: 'object',
  properties: {
    eventId:   { type: 'string' },
    service:   { type: 'string' },
    severity:  { type: 'string', enum: ['info', 'warn', 'error'] },
    latencyMs: { type: 'integer' },
    timestamp: { type: 'string' },
    region:    { type: 'string' }
  },
  required: ['eventId', 'service', 'severity', 'latencyMs', 'timestamp']
})

const event = {
  eventId:   'evt_3c7f9a2b',
  service:   'checkout-api',
  severity:  'warn',
  latencyMs: 342,
  timestamp: new Date().toISOString(),
  region:    'eu-north-1'
}

const json = serializeTelemetryEvent(event)
// '{"eventId":"evt_3c7f9a2b","service":"checkout-api","severity":"warn",...}'

import { inspect } from 'util'

const payload = {
  requestId: "req_7d2e91",
  user: { id: "usr_4421", roles: ["admin", "billing"] },
  metadata: { ipAddress: "203.0.113.42", userAgent: "Mozilla/5.0" },
  createdAt: new Date()
}

// depth: null → expandera alla kapslade nivåer; colors: true → ANSI-terminalfärger
console.log(inspect(payload, { colors: true, depth: null }))

npm install stream-json

import { pipeline } from 'stream/promises'
import { createReadStream } from 'fs'
import { parser } from 'stream-json'
import { streamArray } from 'stream-json/streamers/StreamArray.js'

// events.json = array med miljontals objekt — läses aldrig in helt i minnet
await pipeline(
  createReadStream('./events.json'),
  parser(),
  streamArray(),
  async function* (source) {
    for await (const { value: event } of source) {
      if (event.severity === 'error') {
        console.log(JSON.stringify(event, null, 2))
      }
    }
  }
)

import { createReadStream } from 'fs'
import { createInterface } from 'readline'

// Format: ett JSON-objekt per rad (loggar, Kafka-exporter, BigQuery)
const rl = createInterface({
  input: createReadStream('./logs.ndjson'),
  crlfDelay: Infinity
})

for await (const line of rl) {
  if (!line.trim()) continue
  const entry = JSON.parse(line)
  if (entry.level === 'error') {
    console.log(JSON.stringify(entry, null, 2))
  }
}