Supabase JavaScript Client
Official JavaScript/TypeScript client library for Supabase — the open-source Firebase alternative built on PostgreSQL. Provides a unified client for Supabase's services: PostgreSQL database queries (via PostgREST), Auth (sign-in/JWT/OAuth), Storage (file upload/download), Realtime (websocket subscriptions to DB changes), and Edge Functions. Works in browser, Node.js, React Native, and edge runtimes. TypeScript-first with auto-generated types from your DB schema.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
TLS enforced. RLS provides row-level database security. anon/service_role key separation. JWT-based auth with automatic refresh. SOC2 certified. HIPAA available on Enterprise.
⚡ Reliability
Best When
You're building a JavaScript/TypeScript application on Supabase and want a unified client for database, auth, storage, and realtime without writing separate API wrappers.
Avoid When
You need complex PostgreSQL operations, have an existing backend not on Supabase, or need extreme real-time scale.
Use Cases
- • Query Supabase PostgreSQL tables with a chainable JS API (select, filter, join) without writing raw SQL for typical CRUD operations
- • Implement full authentication flows (email/password, magic link, OAuth with Google/GitHub) using Supabase Auth with automatic JWT management
- • Subscribe to real-time database changes (inserts, updates, deletes) via WebSocket for live-updating agent dashboards and collaboration features
- • Upload and serve files from Supabase Storage with signed URLs, access policies, and CDN distribution
- • Call Supabase Edge Functions (Deno-based serverless) from client or server for custom business logic
Not For
- • Complex PostgreSQL queries requiring raw SQL control — use postgres.js or pg directly for complex queries
- • Non-Supabase backends — supabase-js is tied to Supabase infrastructure; use Apollo Client for GraphQL backends
- • High-frequency realtime at massive scale — Supabase Realtime has scale limits; use dedicated streaming infra for extreme throughput
Interface
Authentication
Two key types: anon key (safe for browser, RLS-protected) and service_role key (admin, server-side only). JWTs issued by Supabase Auth auto-attach to requests. OAuth providers (Google, GitHub, etc.) handled by Supabase Auth. RLS policies enforce data access at DB level.
Pricing
Free tier is generous for development and small apps. Pro adds daily backups and higher limits. Can self-host Supabase open source for no infrastructure cost.
Agent Metadata
Known Gotchas
- ⚠ Always check error field in { data, error } — supabase-js does NOT throw on API errors; must explicitly check 'if (error) throw error' pattern
- ⚠ anon key vs service_role key: anon key is safe for browser (RLS enforced), service_role key bypasses RLS — NEVER expose service_role key in browser code
- ⚠ RLS policies must be enabled and configured for tables — tables without RLS policies are accessible to all authenticated users; new tables have RLS disabled by default
- ⚠ Realtime subscriptions must be explicitly enabled per table in Supabase dashboard — realtime is not auto-enabled for existing tables
- ⚠ File uploads via Storage require correct content-type header — wrong content-type causes serving issues; always specify contentType in upload options
- ⚠ Session handling differs between SSR and client-side — for Next.js/SvelteKit use @supabase/ssr package, not @supabase/supabase-js directly, to handle cookie-based auth correctly
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Supabase JavaScript Client.
Scores are editorial opinions as of 2026-03-06.