TypeScript has rapidly become a popular language for modern web development, yet its effect on software faults remains poorly understood. This paper presents the first large-scale empirical study of bugs in real-world TypeScript projects. We analyze 633 bug reports from 16 popular open-source repositories to construct a taxonomy of fault types, quantify their prevalence, and relate them to project characteristics such as size, domain, and dependency composition. Our results reveal a fault landscape dominated not by logic or syntax errors but by tooling and configuration faults, API misuses, and asynchronous error-handling issues. We show that these categories correlate strongly with build complexity and dependency heterogeneity, indicating that modern failures often arise at integration and orchestration boundaries rather than within algorithmic logic. A longitudinal comparison with JavaScript studies shows that while static typing in TypeScript has reduced traditional runtime and type errors, it has shifted fragility toward build systems and toolchains. These findings offer new insight into how language design and ecosystem evolution reshape the fault profiles of large-scale software systems.

Asynchronous software often exhibits complex and error-prone behaviors that should be tested thoroughly. Code coverage has been the most popular metric to assess test suite quality. However, traditional code coverage criteria do not adequately reflect completion, interactions, and error handling of asynchronous operations. This paper proposes novel test adequacy criteria for measuring: (i) completion of asynchronous operations in terms of both successful and exceptional execution, (ii) registration of reactions for handling both possible outcomes, and (iii) execution of said reactions through tests. We implement JScope, a tool for automatically measuring coverage according to these criteria in JavaScript applications, as an interactive plug-in for Visual Studio Code. An evaluation of JScope on 20 JavaScript applications shows that the proposed criteria can help improve assessment of test adequacy, complementing traditional criteria. According to our investigation of 15 real GitHub issues concerned with asynchrony, the new criteria can help reveal faulty asynchronous behaviors that are untested yet are deemed covered by traditional coverage criteria. We also report on a controlled experiment with 12 participants to investigate the usefulness of JScope in realistic settings, demonstrating its effectiveness in improving programmers’ ability to assess test adequacy and detect untested behavior of asynchronous code.

Program comprehension is a necessary step for performing many software engineering tasks. Dynamic analysis is effective in producing execution traces that assist comprehension. Traces are rich sources of information regarding the behaviour of a program. However, it is challenging to gain insight from traces due to their overwhelming amount of data and complexity. We propose a generic technique for facilitating comprehension by inferring recurring execution motifs. Inspired by bioinformatics, motifs are patterns in traces that are flexible to small changes in execution, and are captured in a hierarchical model. The hierarchical nature of the model provides an overview of the behaviour at a high-level, while preserving the execution details and intermediate levels in a structured manner. We design a visualization that allows developers to observe and interact with the model. We implement our approach in an open-source tool, called Sabalan, and evaluate it through a user experiment. The results show that using Sabalan improves developers' accuracy in performing comprehension tasks by 54%.

Asynchronous client-server communication is a common source of errors in JavaScript web applications. Such errors are difficult to detect using ordinary testing because of the nondeterministic scheduling of AJAX events. Existing automated event race detectors are generally too imprecise or too inefficient to be practically useful. To address this problem, we present a new approach based on a lightweight combination of dynamic analysis and controlled execution that directly targets identification of harmful AJAX event races.

Recently, promises were added to ECMAScript 6, the JavaScript standard, in order to provide better support for the asynchrony that arises in user interfaces, network communication, and non-blocking I/O. Using promises, programmers can avoid common pitfalls of event-driven programming such as event races and the deeply nested counterintuitive control ow referred to as “callback hell”. Unfortunately, promises have complex semantics and the intricate control– and data- ow present in promise-based code hinders program comprehension and can easily lead to bugs. The promise graph was proposed as a graphical aid for understanding and debugging promise-based code. However, it did not cover all promise-related features in ECMAScript 6, and did not present or evaluate any technique for constructing the promise graphs. In this paper, we extend the notion of promise graphs to include all promise-related features in ECMAScript 6, including default reactions, exceptions, and the synchronization operations race and all. Furthermore, we report on the construction and evaluation of PromiseKeeper, which performs a dynamic analysis to create promise graphs and infer common promise anti-patterns. We evaluate PromiseKeeper by applying it to 12 open source promise-based Node.js applications. Our results suggest that the promise graphs constructed by PromiseKeeper can provide developers with valuable information about occurrences of common anti-patterns in their promise-based code, and that promise graphs can be constructed with acceptable run-time overhead.

JavaScript has become one of the most popular languages in practice. Developers now use JavaScript not only for the client-side but also for server-side programming, leading to "full-stack" applications written entirely in JavaScript. Understanding such applications is challenging for developers, due to the temporal and implicit relations of asynchronous and event-driven entities spread over the client and server side. We propose a technique for capturing a behavioural model of full-stack JavaScript applications' execution. The model is temporal and context-sensitive to accommodate asynchronous events, as well as the scheduling and execution of lifelines of callbacks. We present a visualization of the model to facilitate program understanding for developers. We implement our approach in a tool, called Sahand, and evaluate it through a controlled experiment. The results show that Sahand improves developers' performance in completing program comprehension tasks by increasing their accuracy by a factor of three.

JavaScript is one of the most popular programming languages. How- ever, understanding the dynamic behaviour of JavaScript apps is challenging in practice. There are many factors that hinder JavaScript comprehension, such as its dynamic, asynchronous, and event- driven nature, the dynamic interplay between JavaScript and the Document Object Model, and the asynchronous communication between client and server. In this research work, we have already proposed methods for understanding event-based and asynchronous JavaScript behaviour. To enhance the scalability of our methods, we propose a new technique that adopts bio-informatics algorithms to extract sequences of actions from execution traces that form higher-level patterns.

Web applications have become one of the fastest-growing types of software systems today. Despite their popularity, understanding the behavior of modern web applications is still a challenging endeavor for developers during development and maintenance tasks. The challenges mainly stem from the dynamic, event-driven, 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 behavioral 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 C lematis , allows developers to easily understand the complex dynamic behavior of their application at three different semantic levels of granularity. Furthermore, C lematis 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 C lematis is capable of improving the comprehension task accuracy by 157% while reducing the task completion time by 47%. A follow-up experiment reveals that C lematis improves the fault localization accuracy of developers by a factor of two.

JavaScript has grown to be among the most popular programming languages. However, performing change impact analysis on JavaScript applications is challenging due to features such as the seamless interplay with the DOM, event-driven and dynamic function calls, and asynchronous client/server communication. We first perform an empirical study of change propagation, the results of which show that the DOM-related and dynamic features of JavaScript need to be taken into consideration in the analysis since they affect change impact propagation. We propose a DOM-sensitive hybrid change impact analysis technique for Javascript through a combination of static and dynamic analysis. The proposed approach incorporates a novel ranking algorithm for indicating the importance of each entity in the impact set. Our approach is implemented in a tool called Tochal. The results of our evaluation reveal that Tochal provides a more complete analysis compared to static or dynamic methods. Moreover, through an industrial controlled experiment, we find that Tochal helps developers by improving their task completion duration by 78% and accuracy by 223%.

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, event-driven, 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. The results of our industrial controlled experiment show that Clematis is capable of improving the task accuracy by 61%, while reducing the task completion time by 47%.