08 — Proxy passthrough

Mock the routes you're building; forward everything else verbatim to a real backend.

Run this chapter in 30 seconds

1. Open in StackBlitz → — full Node sandbox in your browser, no install.
2. Wait for npm install to finish, then in the Terminal tab run:

   npx tsx examples/08-proxy/server.ts

3. Paste any request from the Try it section below into the Terminal (use curl — the StackBlitz preview port is forwarded).

Concept

proxy.target is the upstream URL. When a request doesn't match any endpoint (or the matching endpoint is disabled), mockr forwards it: same method, path, query, body, and headers. Cookies on the response have Domain= and Secure stripped so they stick on localhost.

Toggle at runtime: server.enableProxy() / disableProxy() / setProxyTarget(url).

Code

import { mockr, mockGroup } from '@yoyo-org/mockr';

const TARGET = process.env.PROXY_TARGET || 'https://jsonplaceholder.typicode.com';

type Endpoints = {
  '/api/feature-flags': { darkMode: boolean; betaSearch: boolean };
  '/api/users/me': { id: number; name: string; role: string };
};

// mock the routes you're working on
const dev = mockGroup<Endpoints>()
  .data('/api/feature-flags', { darkMode: true, betaSearch: true })
  .get('/api/users/me', () => ({ id: 42, name: 'Dev User', role: 'admin' }))
  .done();

mockr({
  port: 3008,
  proxy: { target: TARGET },
  groups: [dev],
});

Try it

Open in StackBlitz → — paste each curl into the StackBlitz Terminal once npx tsx examples/08-proxy/server.ts is running.

# mocked
curl -s http://localhost:3008/api/feature-flags
curl -s http://localhost:3008/api/users/me

# proxied — passthrough to jsonplaceholder
curl -s http://localhost:3008/posts/1
curl -s 'http://localhost:3008/posts?userId=1'

The console tags each line:

  mock  GET    200 /api/feature-flags  3ms
  mock  GET    200 /api/users/me       1ms
   ->   GET    200 /posts/1            142ms

What's next

Forward inside a handler and mutate the response before returning → 09 — ctx.forward().