Web Engine vs. Browser vs. Full Browser vs. JavaScript Engine
Most of this section was written with the help of v8.
Web Engine vs. Browser
A web engine (more commonly called a “browser engine” or “rendering engine”) is not the same as a full web browser, though it’s a core component of one.
A browser engine is the core component responsible for:
- Parsing HTML, CSS, and JavaScript
- Rendering web content
- Implementing web standards
- Handling layout and painting of web pages
A full web browser includes the browser engine plus:
- User interface (address bar, tabs, bookmarks)
- Network stack
- Storage mechanisms
- Extensions/plugins support
- Developer tools
- Security features
Popular Browser Engines
- Blink: Powers Chrome, Edge, Opera, and other Chromium-based browsers
- WebKit: Powers Safari
- Gecko: Powers Firefox
Building a Web Engine vs. Building a Browser
If you’re building a web engine, you’re creating the core rendering technology but not necessarily all the surrounding browser features. Many applications embed web engines to display web content without being full browsers (like Electron apps or in-app browsers).
Building a full browser means implementing both the engine and all the user-facing features that make up the complete browsing experience.
JavaScript Engine vs. Web Engine
SpiderMonkey is not a web engine - it’s a JavaScript engine.
- SpiderMonkey is Mozilla’s JavaScript engine that executes JavaScript code. It was the first JavaScript engine, originally created by Brendan Eich at Netscape.
- A JavaScript engine handles parsing and executing JavaScript code, managing memory, and optimizing performance of JavaScript execution.
- A web engine (like Gecko, WebKit, or Blink) is responsible for rendering the complete web page, including HTML parsing, CSS layout, and integrating with the JavaScript engine.
In Firefox’s architecture:
- Gecko is the web/browser engine
- SpiderMonkey is the JavaScript engine that works within Gecko
Other browser combinations include:
- Chrome: Blink (web engine) + V8 (JavaScript engine)
- Safari: WebKit (web engine) + JavaScriptCore (JavaScript engine)
So while SpiderMonkey is a critical component for processing JavaScript in Firefox, it’s just one part of the complete web rendering pipeline, not a web engine itself.