How Javascript runs in the browser vs. on the server

• Environment: Runs within the browser (e.g., Chrome, Firefox, Safari). Each browser has a built-in Javascript engine (e.g., V8 for Chrome, SpiderMonkey for Firefox).

• Execution Context:

  • Javascript code executes within the web page, often as part of the Document Object Model (DOM).

  • It can manipulate HTML, CSS, and respond to user events (clicks, form submissions).

  • The browser sandbox restricts direct access to the file system, network, and other sensitive parts of the user's device, ensuring security.

• Event-Driven: Javascript in the browser is highly event-driven, reacting to user interactions and events like button clicks, keyboard input, and page loads.

• Asynchronous Operations: Utilizes features like setTimeout, setInterval, fetch, and Promise to handle asynchronous tasks, allowing for non-blocking user experiences.

• Limited Storage: Can store data locally using cookies, localStorage, and sessionStorage.

• Environment: Runs on a server environment like Node.js, which also uses a Javascript engine (V8) but outside the browser context. Node.js provides additional APIs for file systems, networking, and OS interactions.

• Execution Context:

  • Javascript on the server handles tasks like processing HTTP requests, interacting with databases, and generating dynamic content.

  • It has access to the server’s file system, network sockets, and more, enabling it to perform backend operations.

  • Unlike the browser, it doesn’t interact with the DOM directly. Instead, it generates HTML or sends data to the client-side code for rendering.

• Event-Driven, Non-Blocking I/O: Node.js is designed to handle many concurrent connections with non-blocking I/O, making it ideal for real-time applications (e.g., chat apps).

• Scalability: Javascript on the server can handle tasks like authentication, data processing, and API requests, often using frameworks like Express.js or Fastify.

Both environments use Javascript, but their capabilities and use cases vary based on what the application needs to accomplish.