Express Adapter Installation

The Express adapter seamlessly integrates LensJS into your Express application, allowing you to monitor requests, queries, and other events.

1. Install Packages

First, install the Express adapter package:

npm install @lensjs/express

If you plan to use pre-built watcher handlers (e.g., for Prisma), you should also install the @lensjs/watchers package:

npm install @lensjs/watchers

2. Minimal Setup (with Prisma Query Watcher)

Here's a minimal example demonstrating how to set up Lens with an Express application, including a Prisma query watcher:

import { lens } from "@lensjs/express";
import { createPrismaHandler } from "@lensjs/watchers";
import { PrismaClient } from "@prisma/client";
import express from "express";

const app = express();
const port = 3000;
const prisma = new PrismaClient({ log: ["query"] });

await lens({
  app,
  queryWatcher: {
    enabled: true,
    handler: createPrismaHandler({
      prisma,
      provider: "mysql",
    }),
  },
});

app.get("/hello-world", async (_req, res) => {
  await prisma.user.create({ data: { name: "Alice" } });
  res.send("Hello world!");
});

app.listen(port, () => {
  console.log(`Server running on http://localhost:${port}`);
});

Try it out

1. Start your Express application.
2. Visit http://localhost:3000/hello-world in your browser. This will trigger a request and a database query, which Lens will log.
3. Navigate to http://localhost:3000/lens to open the Lens dashboard and view the monitored activity.

3. Next Steps

• Explore more advanced configuration options in the Configuration Guide.