Reactive programming is an emerging programming paradigm where reactive behavior in modern software that periodically responds to changes in surrounding environments is naturally and declaratively represented. One well-known technique for debugging reactive programs is time-traveling where we can pause the execution and rewind to any earlier point in the execution history. On the other hand, anomalies in a data stream often appear in the form where the stream sometimes conveys an error, which may repeat over time. To find such an error, an aid to overview the execution history might help. In this paper, we propose a tool that visualizes the execution history of a program written in a reactive programming language to help the programmer find when suspicious updates of reactive values occur in the history. We also propose a method to record the execution history that makes this visualization possible. Then, we provide a couple of research questions that will be answered in the future work.