Statically identifying class dependencies in legacy JavaScript systems: First results

Identifying dependencies between classes is an essential activity when maintaining and evolving software applications. It is also known that JavaScript developers often use classes to structure their projects. This happens even in legacy code, i.e., code implemented in JavaScript versions that do not provide syntactical support to classes. However, identifying associations and other dependencies between classes remain a challenge due to the lack of static type annotations. This paper investigates the use of type inference to identify relations between classes in legacy JavaScript code. To this purpose, we rely on Flow, a state-of-the-art type checker and inferencer tool for JavaScript. We perform a study using code with and without annotating the class import statements in two modular applications. The results show that precision is 100% in both systems, and that the annotated version improves the recall, ranging from 37% to 51% for dependencies in general and from 54% to 85% for associations. Therefore, we hypothesize that these tools should also depend on dynamic analysis to cover all possible dependencies in JavaScript code.