JavaScript: The Definitive Guide, 6th Edition

Compatibility and Interoperability

The web browser is the operating system for web apps, but the web is a heterogeneous environment and your web documents and applications will be viewed and run in browsers of different ages (from cutting-edge beta releases to decade-old browsers like IE6) from different vendors (Microsoft, Mozilla, Apple, Google, Opera) running on different operating systems (Windows, Mac OS, Linux, iPhone OS, Android). It is challenging to write nontrivial client-side JavaScript programs that run correctly on such a wide variety of platforms.

Client-side JavaScript compatibility and interoperability issues fall into three general categories:

Evolution

The web platform is always evolving and expanding. A standards body proposes a new feature or API. If the feature seems useful, browser vendors implement it. If enough vendors implement it interoperably, developers begin to use and depend on the feature, and it secures a permanent place in the web platform. Sometimes browser vendors and web developers take the lead and standards bodies write the official version well after the feature is already a de facto standard. In either case, a new feature has been added to the Web. New browsers support it and old browsers do not. Web developers are pulled between wanting to use powerful new features and wanting their web pages to be usable by the largest number of visitors—even those who are not using the latest browsers.

Nonimplementation

Sometimes browser vendors differ in their ...