langfuse-js

Modular mono repo for the Langfuse JS/TS client libraries.

Packages

Package	NPM	Environments
langfuse		Node >= 18, Web, Edge
langfuse-node		Node < 18
langfuse-langchain		Node >= 20, Web, Edge

Documentation

→ docs.langfuse.com

Development

This repository is broken into different packages

• /langfuse-core > All common code goes here.
• /langfuse-node > Node.js specific code
• /langfuse > Web/Edge/modern Node.js specific code, using fetch and browser APIs
• /langfuse-langchain > Langchain integration via callback handler

Installing dependencies

yarn

Running tests

yarn test

Integration test

Setup

1. Start local langfuse server
2. Create testing project
3. Set environment: LF_HOST, LF_PUBLIC_KEY, LF_SECRET_KEY

Run

# Build SDKs
yarn build

# Run E2E test
yarn test:integration

Publishing a new version

Run npx lerna publish --force-publish --no-private

• Bumps version number of langfuse and langfuse-node, ignores langfuse-core
• Publishes to NPM, publishes also when there are no changes to keep the version numbers in sync
• Confirm with npmjs OTP

License

MIT

Credits

Thanks to the PostHog team for the awesome work on posthog-js-lite. This project is based on it as it was the best starting point to build a modular SDK repo to support various environments.