URL Encode JavaScript — encodeURIComponent()

// Encode a search query parameter that contains special characters
const searchQuery  = 'Wireless Keyboard & Mouse'
const filterStatus = 'in-stock'
const maxPrice     = '149.99'

const searchUrl = `https://shop.example.com/products?` +
  `q=${encodeURIComponent(searchQuery)}` +
  `&status=${encodeURIComponent(filterStatus)}` +
  `&maxPrice=${encodeURIComponent(maxPrice)}`

console.log(searchUrl)
// https://shop.example.com/products?q=Wireless%20Keyboard%20%26%20Mouse&status=in-stock&maxPrice=149.99

// The redirect destination is itself a URL — it must be fully encoded
// or the outer URL parser will misinterpret its ? and & as its own
const redirectAfterLogin = 'https://dashboard.internal/reports?view=weekly&team=platform'

const loginUrl = `https://auth.company.com/login?next=${encodeURIComponent(redirectAfterLogin)}`

console.log(loginUrl)
// https://auth.company.com/login?next=https%3A%2F%2Fdashboard.internal%2Freports%3Fview%3Dweekly%26team%3Dplatform

// Decoding on the receiving end
const params    = new URLSearchParams(window.location.search)
const next      = params.get('next')              // Automatically decoded
const nextUrl   = new URL(next!)                  // Safe to parse
console.log(nextUrl.hostname)                     // dashboard.internal

// encodeURIComponent handles Unicode natively in all modern environments
// Each UTF-8 byte of the character is percent-encoded
const customerName = 'Kowalski, Tomasz'
const productTitle = 'Warszawa wireless adapter'
const reviewText   = 'Bardzo dobry — działa idealnie'

console.log(encodeURIComponent(customerName))
// Kowalski%2C%20Tomasz

console.log(encodeURIComponent(productTitle))
// Warszawa%20wireless%20adapter

console.log(encodeURIComponent(reviewText))
// Bardzo%20dobry%20%E2%80%94%20dzia%C5%82a%20idealnie

// Decoding back
console.log(decodeURIComponent('Bardzo%20dobry%20%E2%80%94%20dzia%C5%82a%20idealnie'))
// Bardzo dobry — działa idealnie

// A URL pasted from a document with spaces in the path and non-ASCII chars
const rawUrl = 'https://cdn.example.com/assets/product images/München chair.png'

const safeUrl = encodeURI(rawUrl)
console.log(safeUrl)
// https://cdn.example.com/assets/product%20images/M%C3%BCnchen%20chair.png

// encodeURIComponent would break it — it encodes the :// and all / characters
const broken = encodeURIComponent(rawUrl)
console.log(broken)
// https%3A%2F%2Fcdn.example.com%2Fassets%2Fproduct%20images%2FM%C3%BCnchen%20chair.png
// ↑ Not a valid URL — the scheme and slashes are destroyed

// Building a search API URL with multiple parameters
const filters = {
  query:    'standing desk',
  category: 'office-furniture',
  minPrice: '200',
  maxPrice: '800',
  inStock:  'true',
  sortBy:   'price_asc',
}

const params = new URLSearchParams(filters)

const apiUrl = `https://api.example.com/v2/products?${params}`
console.log(apiUrl)
// https://api.example.com/v2/products?query=standing+desk&category=office-furniture&minPrice=200&maxPrice=800&inStock=true&sortBy=price_asc

// Appending additional params after construction
params.append('page', '2')
params.append('tag', 'ergonomic & adjustable')
console.log(params.toString())
// query=standing+desk&...&tag=ergonomic+%26+adjustable

// Both browser (window.location.search) and Node.js (req.url) scenarios
function parseWebhookCallbackUrl(rawSearch: string) {
  const params = new URLSearchParams(rawSearch)

  return {
    eventId:     params.get('event_id'),       // null if missing
    timestamp:   Number(params.get('ts')),
    signature:   params.get('sig'),
    redirectUrl: params.get('redirect'),       // Automatically decoded
    tags:        params.getAll('tag'),         // Handles repeated keys
  }
}

const callbackQuery = '?event_id=evt_9c2f&ts=1717200000&sig=sha256%3Dabc123&redirect=https%3A%2F%2Fdashboard.internal%2F&tag=payment&tag=webhook'

const parsed = parseWebhookCallbackUrl(callbackQuery)
console.log(parsed.redirectUrl)  // https://dashboard.internal/
console.log(parsed.tags)         // ['payment', 'webhook']

async function searchInventory(params: {
  sku?:      string
  warehouse: string
  minStock:  number
  updatedAfter?: Date
}): Promise<{ items: unknown[]; total: number }> {
  const searchParams = new URLSearchParams()

  if (params.sku)          searchParams.set('sku',          params.sku)
  searchParams.set('warehouse',  params.warehouse)
  searchParams.set('min_stock',  String(params.minStock))
  if (params.updatedAfter) searchParams.set('updated_after', params.updatedAfter.toISOString())

  const url = `https://inventory.internal/api/items?${searchParams}`

  const res = await fetch(url, {
    headers: {
      'Authorization': `Bearer ${process.env.INVENTORY_API_KEY}`,
      'Accept':        'application/json',
    },
  })

  if (!res.ok) {
    throw new Error(`Inventory API ${res.status}: ${await res.text()}`)
  }

  return res.json()
}

const results = await searchInventory({
  warehouse:    'eu-west-1',
  minStock:     10,
  updatedAfter: new Date('2025-01-01'),
})

console.log(`Found ${results.total} items`)

// application/x-www-form-urlencoded POST — used by OAuth token endpoints,
// legacy form-submission APIs, and some webhook providers
async function requestOAuthToken(
  clientId:     string,
  clientSecret: string,
  code:         string,
  redirectUri:  string,
): Promise<{ access_token: string; expires_in: number }> {
  const body = new URLSearchParams({
    grant_type:    'authorization_code',
    client_id:     clientId,
    client_secret: clientSecret,
    code,
    redirect_uri:  redirectUri,  // URLSearchParams encodes this automatically
  })

  const res = await fetch('https://oauth.provider.com/token', {
    method:  'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body:    body.toString(),
    // body: body — also works directly in modern environments (Fetch spec accepts URLSearchParams)
  })

  if (!res.ok) {
    const err = await res.json()
    throw new Error(`OAuth error: ${err.error_description ?? err.error}`)
  }

  return res.json()
}

# ── Node.js one-liners — cross-platform (macOS, Linux, Windows) ────────

# encodeURIComponent — encode a single value
node -e "console.log(encodeURIComponent(process.argv[1]))" "Wireless Keyboard & Mouse"
# Wireless%20Keyboard%20%26%20Mouse

# Build a complete query string
node -e "console.log(new URLSearchParams(JSON.parse(process.argv[1])).toString())"   '{"q":"standing desk","category":"office-furniture","page":"1"}'
# q=standing+desk&category=office-furniture&page=1

# Decode a percent-encoded string
node -e "console.log(decodeURIComponent(process.argv[1]))" "Wireless%20Keyboard%20%26%20Mouse"
# Wireless Keyboard & Mouse

# ── curl — automatic encoding ───────────────────────────────────────────
# curl --data-urlencode encodes values automatically in GET and POST
curl -G "https://api.example.com/search"   --data-urlencode "q=Wireless Keyboard & Mouse"   --data-urlencode "category=office furniture"

# ── Python one-liner (available on most systems) ─────────────────────────
python3 -c "from urllib.parse import quote; print(quote(input(), safe=''))"
# (type the string and press Enter)

# ── jq + bash: encode every value in a JSON object ───────────────────────
echo '{"q":"hello world","tag":"node & express"}' |   node -e "const d=JSON.parse(require('fs').readFileSync('/dev/stdin','utf8'));            console.log(new URLSearchParams(d).toString())"
# q=hello+world&tag=node+%26+express

npm install qs
# or
pnpm add qs

import qs from 'qs'

// URLSearchParams cannot represent this structure natively
const reportFilters = {
  dateRange: {
    from: '2025-01-01',
    to:   '2025-03-31',
  },
  status:    ['published', 'archived'],
  author:    { id: 'usr_4f2a9c1b', role: 'editor' },
  workspace: 'ws-platform-eu',
}

// qs produces bracket-notation query strings used by Express, Rails, Django REST
const query = qs.stringify(reportFilters, { encode: true })
console.log(query)
// dateRange%5Bfrom%5D=2025-01-01&dateRange%5Bto%5D=2025-03-31&status%5B0%5D=published&status%5B1%5D=archived&author%5Bid%5D=usr_4f2a9c1b&author%5Brole%5D=editor&workspace=ws-platform-eu

// Human-readable (no encoding) — useful for debugging
console.log(qs.stringify(reportFilters, { encode: false }))
// dateRange[from]=2025-01-01&dateRange[to]=2025-03-31&status[0]=published&status[1]=archived...

// Parsing back
const parsed = qs.parse(query)
console.log(parsed.dateRange)   // { from: '2025-01-01', to: '2025-03-31' }
console.log(parsed.status)      // ['published', 'archived']