clinic.js — TypeScript Application Monitoring

What is clinic.js?

Clinic.js is a powerful tool for monitoring and profiling Node.js applications written in TypeScript and JavaScript. It provides visual diagnostic reports that help identify performance bottlenecks, memory leaks, event loop issues, and asynchronous code problems. The library integrates into the development and operations process, allowing you to analyze application behavior in real time.

Why monitor TypeScript applications?

TypeScript compiles to JavaScript, which runs in the Node.js environment. Complex applications with asynchronous calls, promises, and the event loop can suffer from:

• Slow database queries
• Memory leaks (e.g., due to incorrect caching)
• Event loop blocking (CPU-intensive operations)
• Inefficient algorithms

Clinic.js helps developers visualize these problems so they can quickly find and fix them.

How to install?

Installation via npm/yarn:

npm install -g clinic

Or for use in a project:

npm install --save-dev clinic

After installation, you can run commands in the terminal.

Main Features

• Clinic Doctor — general application diagnostics (CPU, memory, event loop).
• Clinic Bubbleprof — visualization of asynchronous operations and delays.
• Clinic Flame — flame graphs for analyzing code execution hot spots.
• Clinic Heap Profiler — heap profiling for finding memory leaks.
• Integration with Autocannon — load testing combined with profiling.

TypeScript Code Example

Suppose you have an Express server in TypeScript. Start monitoring with clinic doctor:

// server.tsimport express from 'express';

const app = express();

app.get('/', (req, res) => {  // Simulating heavy work  let sum = 0;  for (let i = 0; i < 1e7; i++) {    sum += Math.sqrt(i);  }  res.send('Hello World');});

app.listen(3000, () => console.log('Server started'));

Run profiling:

clinic doctor -- node dist/server.js

After completion (Ctrl+C), an HTML report with CPU, memory, and event loop graphs will open. You will see that the '/' endpoint blocks the event loop due to the synchronous loop. Fix this by using asynchronous processing or Worker Threads.

When to use?

• When optimizing performance — when the application starts to slow down under load.
• During development — for early detection of memory or asynchronicity issues.
• When refactoring — to ensure changes have not degraded performance.
• In CI/CD — for automatic profiling before a release.

Clinic.js is an indispensable tool for those writing TypeScript for Node.js who want to keep performance under control.