Web applications nowadays are present in different domains, from configuration panels of IT devices to the core of large scale enterprise system and are so used by millions of users everyday. Therefore, security plays a key role in their development and use. The purpose of this internship is to understand how web applications programming language particularities impact on the outcomes of Static Application Security Testing (SAST) tools to scan web applications code to figure out vulnerabilities, by producing a series of patterns. This thesis work is focused on JavaScript (JS) language, which is one of the most used today for the development of web applications.