A Understanding JavaScript Event-Based Interactions with Clematis

Web applications have become one of the fastest growing types of software systems today. Despite their popularity, understanding the behaviour of modern web applications is still a challenging endeavour for developers during development and maintenance tasks. The challenges mainly stem from the dynamic, eventdriven, and asynchronous nature of the JavaScript language. We propose a generic technique for capturing low-level event-based interactions in a web application and mapping those to a higher-level behavioural model. This model is then transformed into an interactive visualization, representing episodes of triggered causal and temporal events, related JavaScript code executions, and their impact on the dynamic DOM state. Our approach, implemented in a tool called CLEMATIS, allows developers to easily understand the complex dynamic behaviour of their application at three different semantic levels of granularity. Furthermore, CLEMATIS helps developers bridge the gap between test cases and program code by localizing the fault related to a test assertion. The results of our industrial controlled experiment show that CLEMATIS is capable of improving the comprehension task accuracy by 157%, while reducing the task completion time by 47%. A follow up experiment reveals that CLEMATIS improves the fault localization accuracy of developers by a factor of two.