What are the differences between web browsers in rendering web pages?

Web browsers differ in rendering web pages due to their unique rendering engines, support for web standards, and JavaScript engines.

Each web browser uses a specific rendering engine to interpret the HTML, CSS, and JavaScript of a web page and display it on your screen. For instance, Google Chrome and Opera use the Blink engine, Firefox uses Gecko, and Safari uses WebKit. These engines don't always interpret code in the same way, leading to differences in how a page looks or behaves across different browsers.

Rendering engines are not the only factor that causes differences in web page rendering. The level of support for web standards like HTML5, CSS3, and JavaScript also varies between browsers. Web standards are guidelines developed by the World Wide Web Consortium (W3C) and other organisations to ensure the long-term growth of the web. However, not all browsers support these standards to the same extent or in the same way. This can result in inconsistencies in how a web page appears or functions on different browsers.

JavaScript engines also play a significant role in how web pages are rendered. JavaScript is a programming language commonly used to create interactive effects within web browsers. Each browser has its own JavaScript engine, such as Chrome's V8 engine, Firefox's SpiderMonkey, and Safari's JavaScriptCore. These engines interpret and execute JavaScript code, and their performance can significantly impact how quickly and smoothly web pages load and run.

Moreover, the way a browser handles fallbacks (alternative solutions when a certain feature is not supported) can also affect the rendering of web pages. Some browsers may have built-in fallbacks for certain features, while others may rely on the web developer to provide these fallbacks. This can lead to differences in how a web page is displayed if a particular feature is not supported by a browser.

In conclusion, the differences in web page rendering across browsers can be attributed to their unique rendering engines, varying levels of support for web standards, different JavaScript engines, and the way they handle fallbacks. As a result, web developers often have to test their websites on multiple browsers to ensure consistent performance and appearance.