LINE LIFF (Front-end Framework)

Do not answer LIFF questions from memory — LINE updates APIs frequently and training data is unreliable. Always consult the references below.

Reference for building, reviewing, and debugging LIFF web apps inside LINE.

Workflow

Build

1. Read references/guidelines.md (registration, endpoint URL rules, environment compatibility)
2. Load the relevant reference for the feature being implemented
3. For architecture or design choices, consult references/experts.md for directional guidance
4. Write code following specs and constraints from references

Review / Debug

1. Read references/guidelines.md (URL constraints, authentication flow, API availability)
2. Load relevant references for the code being reviewed
3. Cross-check code against specs (endpoint URL rules, scope requirements, environment limitations, init order)
4. For design pattern concerns, consult references/experts.md
5. Report violations with reference to specific constraints

Environment Variables

LIFF_ID=LIFF app ID (from LINE Developers Console)
LINE_LOGIN_CHANNEL_ID=LINE Login Channel ID (for server-side JWT verification)
LINE_LOGIN_CHANNEL_SECRET=Channel secret (server-side only)
CHANNEL_ACCESS_TOKEN=Channel access token (for LIFF Server API — manage LIFF apps programmatically)

SDK

Install via CDN or npm. For tree-shaking (reduce ~34% bundle size), use pluggable SDK.

SDK installation, CDN/npm setup, pluggable SDK → references/api.md § Pluggable SDK

Initialization

liff.init({ liffId: 'YOUR_LIFF_ID', withLoginOnExternalBrowser: true })
  .then(() => { /* use LIFF APIs */ })
  .catch(err => console.error(err.code, err.message));

• Must be called before all LIFF APIs (except pre-init methods)
• withLoginOnExternalBrowser: true — auto-trigger login in external browser
• liff.ready — Promise that resolves when init completes

Getting Started

1. Create a LINE Login channel in LINE Developers Console
2. Add a LIFF app and set the Endpoint URL (HTTPS required)
3. Integrate SDK, call liff.init()
4. Or scaffold with npx @line/create-liff-app (React/Vue/Svelte/Next.js/Nuxt/vanilla)

Core API Summary

Authentication & Profile

Method	Description	Scope
liff.isLoggedIn()	Check login status	—
liff.login()	Trigger login (external browser only)	—
liff.logout()	Log out	—
liff.getProfile()	Get userId, displayName, pictureUrl	profile
liff.getDecodedIDToken()	Get decoded JWT (email, etc.)	openid + email
liff.getIDToken()	Get raw JWT (for server verification)	openid
liff.getFriendship()	Check friendship with linked OA	profile

Messaging

Method	Description	Restriction
liff.sendMessages([...])	Send to current chat (max 5)	LIFF browser only
liff.shareTargetPicker([...])	Pick friends/groups to share	Check isApiAvailable first

Device & Navigation

Method	Description
liff.scanCodeV2()	QR code scanner (enable in Console)
liff.openWindow({url, external})	Open URL
liff.closeWindow()	Close LIFF (unreliable in external browser)

Context

Method	Description
liff.getContext()	Get type, userId, groupId, roomId, viewType
liff.getOS()	'ios', 'android', 'web'
liff.isInClient()	Whether running in LINE app
liff.permanentLink.createUrlBy(url)	Create permanent link

View Sizes

Type	Coverage
Full	100% screen
Tall	~75%
Compact	~50%

Key Constraints

• Endpoint URL: liff.init() only works at or below the registered Endpoint URL
• URL handling: modify URLs only after liff.init() resolves
• Universal Links: use https://liff.line.me/{liffId} as primary entry point
• Token security: send raw ID Token to server for verification, never expose decoded token → see server-auth.md
• Login behavior differs: auto in LIFF browser, manual in external browser
• Deprecated APIs: liff.scanCode() → use scanCodeV2(); liff.getLanguage() → use getAppLanguage(); liff.permanentLink.createUrl() → use createUrlBy() (may be removed in v3)

Reference Index

File	Topic
references/api.md	LIFF v2 API complete reference, pluggable SDK modules, error codes
references/guidelines.md	Registration, endpoint URL rules, authentication flow, UI/UX, environment compatibility
references/navigation.md	LIFF URLs, liff.state, permanent links, LIFF-to-LIFF transitions, browser minimization
references/plugins.md	LIFF plugin development, hooks system, official plugins (Inspector, Mock)
references/server-api.md	LIFF Server API (v1) — programmatic LIFF app CRUD (create, update, list, delete)
references/server-auth.md	Server-side ID Token (JWT) verification
references/cli.md	LIFF CLI — local HTTPS dev server, app CRUD, Inspector debugging, ngrok
references/experts.md	LIFF domain experts for architecture guidance

SDK & Tools

• npm: @line/liff
• Pluggable SDK: @line/liff/core + individual modules
• Official plugins: @line/liff-inspector | @line/liff-mock
• LIFF CLI: CLI tool (create, serve, deploy, HTTPS dev server)
• Create LIFF App: npx @line/create-liff-app — scaffolding (React/Vue/Svelte/Next.js/Nuxt/vanilla, JS/TS)
• LIFF Playground: liff-playground.netlify.app — online API testing
• Starter app: line/line-liff-v2-starter (vanilla/Next.js/Nuxt)