Static Analysis of Dynamic Languages

Dynamic programming languages are highly popular and widely used. Java-Script is often called the lingua franca of the web and it is the de facto standard for client-side web programming. On the server-side the PHP, Python and Ruby languages are prevalent. What these languages have in common is an expressive power which is not easily captured by any static type system. These, and similar dynamic languages, are often praised for their ease-of-use and flexibility. Unfortunately, this dynamism comes at a great cost: The lack of a type system implies that most errors are not discovered until run-time. Thus, in the worst-case, these bugs are not uncovered before they are encountered by real users of the system. A further cost is limited tool support: For instance, integrated development environments with code completion, code navigation and automatic refactorings are widely available for languages with static type systems, such as Java and C], but the same features are rarely available for dynamic languages such as JavaScript