Embodiments of the present invention provide techniques for tracking the lifecycles of client-side browser windows in the context of a web application. In one set of embodiments, a server component of a web application can receive a notification that an application page in a first window has been unloaded/destroyed. In response, the server component can associate the first window with an expiration time and add the first window to an “expiration” list of windows that are potentially inactive. If a request is received by the server component from the first window while the first window is in the expiration list, the server component can identify the first window as active and remove it from the list. If a request is received by the server component from a second window after the expiration time associated with the first window, the server component can identify the first window as inactive and free all resources for the first window.