@codebygarv/express-lens

@codebygarv/express-lens

A lightweight, plug-and-play monitoring package for Express.js applications. It silently tracks your application's metrics and logs a concise analytics summary inline to the console for every HTTP request.

Features

• Zero setup: Just plug it into your Express app as a middleware.
• Dual Support: Natively supports both CommonJS (require) and ES Modules (import).
• Inline Analytics Logs: View realtime metrics for every request without any dashboards getting in the way.
• Performance Tracking: Measures response times, average request durations, and memory (RSS) usage.
• Error Tracking: Keeps a tally of request errors (HTTP 400+).
• Route Specific Metrics: Keeps track of min, max, and total duration per route.

Installation

You can install @codebygarv/express-lens using npm or yarn:

npm install @codebygarv/express-lens

or with Yarn:

yarn add @codebygarv/express-lens

Usage

This package supports both CommonJS and ES Modules.

CommonJS (CJS)

const express = require('express');
const monitor = require('@codebygarv/express-lens');

ES Modules (ESM)

import express from 'express';
import monitor from '@codebygarv/express-lens';

Example Setup

const app = express();

// Add the monitor middleware
app.use(monitor());

// Your routes
app.post('/users', (req, res) => {
  res.status(201).json({ message: 'User created' });
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Example Console Output

When a request hits your server, you will see a log similar to this in your console:

[Analytics] GET /users -> 201 (15.42ms) | Total Reqs: 120 | Errors: 0 | Avg: 22.10ms | Mem: 45.21MB

Configuration

The monitor middleware takes an optional configuration object.

app.use(monitor({
  logAnalytics: true, // Default is true. Set to false to disable console logging entirely.
  logInterval: 0      // Default is 0 (logs every request). Set to > 0 (in milliseconds) for batched logging.
}));

High Performance Mode (Batched Logging)

If your API receives high traffic (e.g., 100+ requests per second), logging every single request will cause significant I/O overhead. You can enable batched logging by passing a logInterval (in milliseconds).

app.use(monitor({
  logInterval: 5000 // Logs a summary of the last 5 seconds instead of every individual request
}));

Example Output with logInterval: 5000:

[Analytics Summary] Interval Reqs: 1250 | Total Reqs: 15000 | Errors: 5 | Avg: 22.10ms | Mem: 45.21MB

Exported Metrics

Internally, express-lens tracks the following data:

Metric	Description
Total Requests	Count of all incoming HTTP requests
Total Errors	Count of responses with status >= 400
Avg Duration	Average response time across all endpoints
Memory (RSS)	Current Resident Set Size of the Node process
Route Metrics	Counts, and min/max durations separated by route

License

MIT

Developed by github/codebygarv