Third-party JavaScript applications are self-contained components, typically small scripts or widgets, that add functionality to websites. As the name implies, they're offered by independent organizations, with code and asset files served from a remote web address.

Third-party JavaScript development is booming. Facebook's "Like" widget is a staple of news websites and blogs, and Twitter's @anywhere components recreate the Twitter experience on any site. Eventbrite, provides embeddable event registration forms that integrate with host websites.

Writing third-party applications poses unique challenges, though. The best applications must adapt seamlessly to a wide variety of host environments. Browsers may not trust code served from different domains, your JavaScript and CSS has to co-exist with other applications, and there are some tricky security vulnerabilities. This book distills the insights and experience of third-party JavaScript experts Ben Vinegar and Anton Kovalyov, developers at Disqus.

Third-Party JavaScript guides web developers through the complete development of a full-featured third-party JavaScript application. You'll learn dozens of techniques for developing widgets that collect data for analytics, provide helpful overlays and dialogs, or implement features like chat or commenting. The concepts and examples throughout this book represent the best practices for this emerging field, based on thousands of real-world dev hours and results from millions of users.