What is SonarJS good for? How does it work internally and how to use it to prevent bugs? An introduction to the ins and outs of the SonarJS code analyzer. After a live demo of the usage of SonarJS within an IDE, we will look into what it means to build a code analyzer and how JavaScript code is represented and understood at different levels of abstraction. And finally we will see how to execute JavaScript code without its actual execution, which is our way to detect runtime exceptions statically.