When you write JavaScript, the environment where your code runs significantly affects what you can do and how your code interacts with the outside world. The two most common environments for JavaScript are Node.js and web browsers. Understanding the differences between these environments will help you choose the right tools and approaches for your projects.

Node.js vs Browser JavaScript Key Differences

Environment

• Node.js runs JavaScript on the server, outside of any browser;
• Browsers run JavaScript on the client side, directly inside the user's web page.

APIs and Built-in Modules

• Node.js includes APIs for working with the file system, networking, and running processes;
• Browsers provide APIs for manipulating the web page (DOM), handling user events, and interacting with the web.

Typical Applications

• Node.js is used to build server-side applications, command-line tools, and scripts;
• Browser JavaScript is used to create interactive web pages and user interfaces.

Security and Permissions

• Node.js scripts can access the local file system and network by default;
• Browser JavaScript is sandboxed for security, limiting access to the user's device.

Global Objects

• Node.js provides global objects like global, process, and Buffer;
• Browsers provide objects like window, document, and navigator.

These differences mean that code written for Node.js often cannot run in the browser without changes, and vice versa.