Stefan Judis Twitter speaker

Watch your back, Browser! You're being observed

Web development can be tough. DOM APIs are known to be inconvenient, and we often build the same things over and over again. Thanks to rolling releases by browser vendors this changed. Development of the web as a platform has sped up like never before. New APIs land in browsers with every release allowing for “reactive programming” through new Observer and Observable APIs. Looking for a way to detect DOM changes to update a different part of the page? MutationObserver got you covered. Want to get notified when elements enter the viewport to load assets? IntersectionObserver is your friend. Are you dealing with sequences of events over time and want to save yourself some headaches? Observables will make your life way easier. During this talk we’ll cover the use cases of Observer/Observable APIs, go over implementation details, and cover everything you need to know to use them in production.


Stefan started programming 7 years ago and quickly fell in love with web performance, new technologies and automation. He worked for several startups in Berlin and recently joined Contentful to tell the world how an API-first CMS can make you a bit happier. He is also a curator of the web performance online resource Perf Tooling (, organizer of the Web Performance Meetup Berlin, contributes to a variety of open source projects and enjoys sharing nerdy discoveries.