Current web browser debuggers are inadequate for today's complex, event-driven, and nondeterministic web applications. The Timelapse project adapts "back-in-time" debugging techniques to the domain of client-side web programming. Unlike traditional breakpoint debuggers, Timelapse creates an exact recording of a web program's execution. This recording can be then played forward and backward and freely inspected at any time, using existing debugging tools. Timelapse also introduces novel trace analyses that help developers navigate execution recordings more efficiently.