Debugging JavaScript has traditionally been non-trivial. This is partly to do with evented asynchronous paradigms inherent in the programming model and partly to do with tooling (and the difficulties in creating tooling that is well matched with JavaScript's programming model).

In recent years, however, as JavaScript usage has exponentially increased in both browser and server-side development, tooling has improved and continues to improve.

In this chapter, we talk about how to use fundamental debugging tools, introduce some additional useful introspection resources, and delve deeper into advanced production debugging tools and techniques such as async tracing and postmortems.