Node.js is a platform built on Chrome’s JavaScript runtime for easily building fast, scalable network applications. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices.

To install it to windows 7 follow these steps :

1. Download .msi file from Node.js (installation file for windows), and install node.js on your computer
2. After that go to System variables and add new one “NODE_PATH”

3. Extend Path system variable so you can use node in all folders

4. Open your command prompt window and point to directory where node is installed. Run following command

npm install mysql

Since you changed system variables you need to restart your system so they can make effect.
Enjoy!