Node.js Event Loop Utilization & Delay Demos

A small practical repo to explore Node.js Event Loop performance using perf_hooks and eventLoopUtilization.

Note: For detailed explanations of each demo, including the code logic and expected behavior, see the 00-readme.md file inside the codes/ folder.

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Overview

This repository demonstrates:

• Measuring Event Loop utilization (ELU)
• Monitoring tick time and mean delay
• Understanding how heavy synchronous tasks affect the event loop
• Dividing heavy tasks into chunks to prevent blocking

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Installation

git clone https://github.com/Maryam-Skaik/nodejs-eventloop-perf.git
cd nodejs-eventloop-perf
npm install

Requires Node.js 14+

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Demos

1. Event Loop Utilization

demo-eventloop-utilization.js Shows ELU metrics: idle, active, utilization, and mean delay. Helps detect ticks overloaded by heavy tasks or microtasks.

2. Chunking Heavy Code

demo-heavy-task-chunks.js Demonstrates splitting a heavy synchronous loop into smaller chunks using setImmediate to reduce tick length and prevent starvation.

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Key Concepts

• utilization: Percentage of time the loop is busy.
• mean delay: Average delay between ticks.
• Tick time: Actual time a tick took.
• Tick capacity: Maximum amount of work a tick can handle before deferring tasks to the next tick.

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Usage

Run a demo:

node codes/demo-eventloop-utilization.js
node codes/demo-heavy-task-chunks.js

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Learning Outcome

• Understand how Node.js event loop handles heavy tasks
• Measure and interpret ELU metrics in real code
• Learn how to split tasks to avoid blocking the loop

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📜 License

This project is licensed under the MIT License
© 2025 Maryam Skaik

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👩‍💻 Author

Maryam Skaik
GitHub Profile | LinkedIn