In 2001, Douglas Crockford named and documented JSON (JavaScript Object Notation), whose main idea is to use JavaScript syntax to store data in text format. JSON uses JavaScript literals for objects, arrays, strings, numbers, and booleans to represent structured data. For example:

{
    "first": "Jane",
    "last": "Porter",
    "married": true,
    "born": 1890,
    "friends": [ "Tarzan", "Cheeta" ]
}

Over the years, JSON has become a popular lightweight alternative to XML, especially when structured data is to be represented and not markup. Naturally, JSON is easy to consume via JavaScript (see Chapter 22).

Ajax is a collection of technologies that brings a level of interactivity to web pages that rivals that of desktop applications. One impressive example of what can be achieved via Ajax was introduced in February 2005: Google Maps. This application allowed you to pan and zoom over a map of the world, but only the content that was currently visible was downloaded to the browser. After Google Maps came out, Jesse James Garrett noticed that it shared certain traits with other interactive websites. He called these traits Ajax, a shorthand for Asynchronous JavaScript and XML.^[7] The two cornerstones of Ajax are loading content asynchronously in the background (via XMLHttpRequest) and dynamically updating the current page with the results (via dynamic HTML). That was a considerable usability improvement from always performing complete page reloads.

Ajax marked the mainstream breakthrough of JavaScript and dynamic web applications. It is interesting to note how long that took—at that point, the Ajax ingredients had been available for years. Since the inception of Ajax, other data formats have become popular (JSON instead of XML), other protocols are used (e.g., Web Sockets in addition to HTTP), and bidirectional communication is possible. But the basic techniques are still the same. However, the term Ajax is used much less these days and has mostly been replaced by the more comprehensive terms HTML5 and Web Platform (which both mean JavaScript plus browser APIs).

Node.js lets you implement servers that perform well under load. To do so, it uses event-driven, nonblocking I/O and JavaScript (via V8). Node.js creator Ryan Dahl mentions the following reasons for choosing JavaScript:

Dahl was able to build on prior work on event-driven servers and server-side JavaScript (mainly the CommonJS project).

The appeal of Node.js for JavaScript programmers goes beyond being able to program in a familiar language; you get to use the same language on both client and server. That means you can share more code (e.g., for validating data) and use techniques such as isomorphic JavaScript. Isomorphic JavaScript is about assembling web pages on either client or server, with numerous benefits: pages can be rendered on the server for faster initial display, SEO, and running on browsers that either don’t support JavaScript or a version that is too old. But they can also be updated on the client, resulting in a more responsive user interface.

With Chrome OS, the web platform is the native platform. This approach has several advantages:

The introduction of the mobile operating system webOS (which originated at Palm and is now owned by LG Electronics) predates the introduction of Chrome OS, but the “browser as OS” idea is more apparent with the latter (which is why it was chosen as a milestone). webOS is both less and more. Less, because it is very focused on cell phones and tablets. More, because it has Node.js built in, to let you implement services in JavaScript. A more recent entry in the web operating system category is Mozilla’s Firefox OS, which targets cell phones and tablets. Mozilla’s wiki mentions a benefit of web operating systems for the Web: