Express

Instrumenting an Express application with Logfire is straightforward. You can use the logfire package to set up logging and monitoring for your Express routes.

app.ts

import express, type { Express } from 'express';

const PORT: number = parseInt(process.env.PORT || '8080');
const app: Express = express();

function getRandomNumber(min: number, max: number) {
  return Math.floor(Math.random() * (max - min + 1) + min);
}

app.get('/rolldice', (req, res) => {
  res.send(getRandomNumber(1, 6).toString());
});

app.listen(PORT, () => {
  console.log(`Listening for requests on http://localhost:${PORT}`);
});

To get started, install the logfire and dotenv NPM packages. This will allow you to keep your Logfire write token in a .env file:

Terminal

npm install logfire dotenv

Add your token to the .env file:

.env

LOGFIRE_TOKEN=your-write-token

Then, create an instrumentation.ts file to set up the instrumentation. The logfire package includes a configure function that simplifies the setup:

instrumentation.ts

import * as logfire from "logfire";
import "dotenv/config";

logfire.configure();

The logfire.configure call should happen before importing the actual Express module, so your NPM start script should look like this in package.json. Note that we use npx ts-node to run the TypeScript code directly:

package.json

"scripts": {
  "start": "npx ts-node --require ./instrumentation.ts app.ts"

A working example can be found in the examples/express directory of the pydantic/logfire-js repository.