Eliminating Code Duplication in Cascading Style Sheets

Cascading Style Sheets (i.e., CSS) is the standard styling language, widely used for defining the presentation semantics of user interfaces for web, mobile and desktop applications. Despite its popularity, CSS has not received much attention from academia. Indeed, developing and maintaining CSS code is rather challenging, due to the inherent language design shortcomings, the interplay of CSS with other programming languages (e.g., HTML and JavaScript), the lack of empirically- evaluated coding best-practices, and immature tool support. As a result, the quality of CSS code bases is poor in many cases. In this thesis, we focus on one of the major issues found in CSS code bases, i.e., the duplicated code. In a large, representative dataset of CSS code, we found an average of 68% duplication in style declarations. To alleviate this, we devise techniques for refactoring CSS code (i.e., grouping style declarations into new style rules), or migrating CSS code to take advantage of the code abstraction features provided by CSS preprocessor languages (i.e., superset languages for CSS that augment it by adding extra features that facilitate code maintenance). Specifically for the migration transformations, we attempt to align the resulting code with manually-developed code, by relying on the knowledge gained by conducting an empirical study on the use of CSS preprocessors, which revealed the common coding practices of the developers who use CSS preprocessor languages. To guarantee the behavior preservation of the proposed transformations, we come up with a list of preconditions that should be met, and also describe a lightweight testing technique. By applying a large number of transformations on several web sites and web applications, it is shown that the transformations are indeed presentation-preserving, and can effectively reduce the amount of duplicated code in CSS

Discovering refactoring opportunities in cascading style sheets

Cascading Style Sheets (CSS) is a language used for describ-ing the look and formatting of HTML documents. CSS has been widely adopted in web and mobile development prac-tice, since it enables a clean separation of content from pre-sentation. The language exhibits complex features, such as inheritance, cascading and specificity, which make CSS code hard to maintain. Therefore, it is important to find ways to improve the maintainability of CSS code. In this paper, we propose an automated approach to remove duplication in CSS code. More specifically, we have developed a technique that detects three types of CSS declaration duplication and recommends refactoring opportunities to eliminate those du-plications. Our approach uses preconditions that ensure the application of a refactoring will preserve the original docu-ment styling. We evaluate our technique on 38 real-world web systems and 91 CSS files, in total. Our findings show that duplication in CSS code is widely prevalent. Addition-ally, there is a significant number of presentation-preserving refactoring opportunities that can reduce the size of the CSS files and increase the maintainability of the code