BrowserSync sets up a proxy to our Express application's static file server and injects additional logic that configures a web socket connection between it and BrowserSync. When multiple devices are connected to the same BrowserSync server, interactions are mirrored and sent to the other devices. This allows interactions such as scrolling, clicking, and page navigation to stay in sync across multiple devices.

You can configure which types of interactions you want to see synchronized across devices under the Sync Options section:

The real potential of a utility such as BrowserSync comes from being able to run multiple browsers through the same set of interactions and quickly see what works and what doesn't. It can also serve as an integration utility for doing automated cross-browser testing when you start creating acceptance tests for your application.