feat(js): add "fetch" plugin by Ehesp · Pull Request #4802 · firebase/genkit

Ehesp · 2026-02-21T21:09:27Z

While Genkit currently supports Express, the modern JavaScript ecosystem is rapidly consolidating around Web Standard APIs (Request, Response, Headers). This PR introduces a new plugin that allows Genkit flows to be exposed via the Fetch API standard, making Genkit natively compatible with virtually every modern JS runtime and framework.

By moving away from Node-specific HTTP abstractions, Genkit can now run seamlessly at the Edge, in Serverless environments, and in high-performance runtimes like Bun and Deno:

Runtimes:

Bun
Deno
Cloudflare Workers (Workerd)
Node (18+) via fetch
Edge (Vercel, Netlify, Fastly)
... and probably more

Frameworks:

Hono
Elysia
Astro
Remix
Nitro (+ frameworks built on-top of it)
TanStack Start
... and probably more

Usage (e.g. Hono):

const app = new Hono();

// Mount a single flow
app.all('/myFlow', (c) => handleFlow(c.req.raw, myFlow));

// Mount Genkit flows under /api - handleFlows routes by path
app.all('/api/*', (c) => handleFlows(c.req.raw, flows, '/api'));

This PR also includes a sample js-hono.

Checklist (if applicable):

PR title is following https://www.conventionalcommits.org/en/v1.0.0/
Tested (manually, unit tested, etc.)
Docs updated (updated docs or a docs bug required)

TODO:

Not sure on the plugin name web - might be a bit too generic.

gemini-code-assist · 2026-02-21T21:09:48Z

Summary of Changes

Hello @Ehesp, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly expands Genkit's deployment flexibility by introducing a new web plugin. This plugin leverages Web Standard APIs to enable Genkit flows to run efficiently across diverse JavaScript environments, from edge functions to serverless platforms and various modern frameworks. It streamlines the process of exposing Genkit functionalities over HTTP, providing robust tools for handling requests, managing context, and supporting durable streaming, thereby broadening Genkit's ecosystem integration capabilities.

Highlights

New Web Plugin Introduction: Introduced a new @genkit-ai/web plugin that enables Genkit flows to be exposed via Web Standard APIs (Request, Response, Headers), making Genkit compatible with a wide array of modern JavaScript runtimes and frameworks.
Broad Runtime and Framework Compatibility: The plugin allows Genkit to run seamlessly at the Edge, in Serverless environments, and high-performance runtimes like Bun and Deno, as well as frameworks such as Hono, Elysia, Astro, and Remix, by moving away from Node-specific HTTP abstractions.
Core API for Flow Handling: Provided handleFlow for single flow execution and handleFlows for routing multiple flows based on URL paths, both designed to work with standard Web API Request and Response objects.
Enhanced Flow Configuration: Added withFlowOptions to wrap flows with custom configurations, including context providers for authentication and stream managers for durable streaming, allowing for more flexible and robust flow deployments.
Durable Streaming Support: Implemented durable streaming capabilities, allowing clients to disconnect and reconnect to a stream without losing state, with options for both in-memory and production-ready stream managers.
New Hono Sample Application: Included a new sample application (js-hono) demonstrating how to integrate Genkit flows with the Hono framework using the new web plugin, showcasing practical usage with authentication and streaming examples.

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Changelog

js/plugins/web/.npmignore
- Added ignore rules for build artifacts and configuration files.
js/plugins/web/README.md
- Added comprehensive documentation detailing installation, usage examples (single/multiple flows, auth, durable streaming, client-side calling), and an API summary for the new web plugin.
js/plugins/web/package.json
- Defined the new @genkit-ai/web package, including metadata, scripts, and peer dependencies.
js/plugins/web/src/index.ts
- Implemented core functions handleFlow and handleFlows for processing Web API requests, withFlowOptions for flow customization, and logic for streaming and durable streaming.
js/plugins/web/src/utils.ts
- Added utility functions getErrorMessage and getErrorStack for consistent error handling.
js/plugins/web/tests/web_test.ts
- Added extensive unit tests covering handleFlow and handleFlows functionalities, including various input types, authentication, streaming, and durable streaming scenarios.
js/plugins/web/tsconfig.json
- Added TypeScript configuration for the new web plugin.
js/plugins/web/tsup.config.ts
- Added tsup build configuration for the new web plugin.
js/plugins/web/typedoc.json
- Added TypeDoc configuration for generating API documentation for the web plugin.
js/pnpm-lock.yaml
- Updated the pnpm lockfile to include new dependencies and reflect changes from the added web plugin and Hono sample.
samples/js-hono/.gitignore
- Added a .gitignore file for the new Hono sample to exclude build artifacts and node modules.
samples/js-hono/README.md
- Added documentation for the new js-hono sample, explaining its setup, usage, and how it integrates Genkit with Hono using the web plugin.
samples/js-hono/package.json
- Defined the new js-hono sample package, including dependencies on @genkit-ai/web and Hono, and scripts for development and building.
samples/js-hono/src/index.ts
- Implemented a Hono server that exposes several Genkit flows (hello, greeting, streaming, secureGreeting) using the new @genkit-ai/web plugin, demonstrating context providers and streaming.
samples/js-hono/tsconfig.json
- Added TypeScript configuration for the new js-hono sample application.
samples/package.json
- Updated the build:all-samples script to include the new js-hono sample build process.

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Code Review

This pull request introduces a new 'web' plugin for Genkit, enabling compatibility with modern Web Standard APIs (Request/Response). This allows Genkit flows to run on various runtimes like Bun, Deno, and Cloudflare Workers. The implementation is solid and well-integrated with Genkit's core concepts. I have identified a few issues regarding path routing logic, error logging robustness, and cross-runtime compatibility that should be addressed.

js/plugins/web/src/index.ts

js/plugins/fetch/src/index.ts

js/plugins/web/src/index.ts

js/plugins/web/README.md

Ehesp · 2026-02-24T19:37:51Z

Sample CI check failing due to the new package not being published (I think!)

pavelgj · 2026-02-25T16:26:47Z

js/plugins/fetch/src/index.ts

+  type RequestData,
+} from 'genkit/context';
+import { logger } from 'genkit/logging';
+import { getErrorMessage, getErrorStack } from './utils';


Suggested change

import { getErrorMessage, getErrorStack } from './utils';

import { getErrorMessage, getErrorStack } from './utils.js';

Ehesp added 3 commits February 21, 2026 19:52

feat(js): add web-standards plugin

485702c

chore: add js-hono example

6550637

docs(js): add web plugin readme

1df6c8a

github-project-automation bot added this to Genkit Backlog Feb 21, 2026

github-actions bot added docs Improvements or additions to documentation js config sample labels Feb 21, 2026

gemini-code-assist bot reviewed Feb 21, 2026

View reviewed changes

pavelgj reviewed Feb 23, 2026

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js/plugins/web/README.md Outdated Show resolved Hide resolved

Ehesp added 5 commits February 24, 2026 17:59

chore(js/plugins/fetch): rename web -> fetch

eb10428

fix: handle review feedback

cdf74d5

chore: formatting

c6ab30e

chore: revert unrelated sample changes

666b640

chore: formatting

bcd26a8

Ehesp marked this pull request as ready for review February 24, 2026 19:37

Ehesp requested review from ifielker and ssbushi as code owners February 24, 2026 19:37

Ehesp changed the title ~~feat(js): add "web" plugin~~ feat(js): add "fetch" plugin Feb 24, 2026

pavelgj reviewed Feb 25, 2026

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feat(js): add "fetch" plugin #4802

feat(js): add "fetch" plugin #4802
Ehesp wants to merge 8 commits intofirebase:mainfrom
Ehesp:js-web-plugin

Ehesp commented Feb 21, 2026 •

edited

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	import { getErrorMessage, getErrorStack } from './utils';
	import { getErrorMessage, getErrorStack } from './utils.js';

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Ehesp commented Feb 21, 2026 •

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