Fix Memory Leaks in Node.js Applications

Identify and fix common Node.js memory leak patterns:

Step 1: Monitor Memory Usage

// Add memory monitoring
function logMemoryUsage() {
    const used = process.memoryUsage();
    console.log('Memory Usage:');
    for (let key in used) {
        console.log(`${key}: ${Math.round(used[key] / 1024 / 1024 * 100) / 100} MB`);
    }
}

// Log every 30 seconds
setInterval(logMemoryUsage, 30000);

Step 2: Fix Event Listener Leaks

// ❌ Problem - event listeners not removed
function createUser(userId) {
    const user = new EventEmitter();

    // This listener is never removed
    user.on('update', handleUpdate);

    return user;
}

// ✅ Solution - properly remove listeners
function createUser(userId) {
    const user = new EventEmitter();

    function handleUpdate(data) {
        // Handle update
    }

    user.on('update', handleUpdate);

    // Cleanup function
    user.cleanup = () => {
        user.removeListener('update', handleUpdate);
        user.removeAllListeners();
    };

    return user;
}

Step 3: Fix Timer and Interval Leaks

// ❌ Problem - timers not cleared
function startPolling() {
    setInterval(() => {
        fetchData();
    }, 5000);
}

// ✅ Solution - clear timers properly
function startPolling() {
    const intervalId = setInterval(() => {
        fetchData();
    }, 5000);

    // Return cleanup function
    return () => clearInterval(intervalId);
}

// Usage
const stopPolling = startPolling();
// Later, when no longer needed:
stopPolling();

Step 4: Handle Stream Cleanup

// ❌ Problem - streams not properly closed
function processFile(filename) {
    const readStream = fs.createReadStream(filename);
    const writeStream = fs.createWriteStream('output.txt');

    readStream.pipe(writeStream);
    // Streams might not be properly closed
}

// ✅ Solution - ensure proper cleanup
function processFile(filename) {
    return new Promise((resolve, reject) => {
        const readStream = fs.createReadStream(filename);
        const writeStream = fs.createWriteStream('output.txt');

        readStream.on('error', (err) => {
            cleanup();
            reject(err);
        });

        writeStream.on('error', (err) => {
            cleanup();
            reject(err);
        });

        writeStream.on('finish', () => {
            cleanup();
            resolve();
        });

        function cleanup() {
            readStream.destroy();
            writeStream.destroy();
        }

        readStream.pipe(writeStream);
    });
}

Step 5: Use Memory Profiling Tools

# Install clinic.js for memory profiling
npm install -g clinic

# Profile your application
clinic doctor -- node app.js

# Or use built-in Node.js inspector
node --inspect app.js
# Then open Chrome DevTools for memory profiling