Java Script is a scripting language that plays a prominent role in modern web applications today. It is dynamic, loosely typed, and asynchronous. In addition, it is extensively used to interact with the DOM at runtime. All these characteristics make Java Script code error-prone and challenging to debug. Java Script fault localization is currently a tedious and mainly manual task. Despite these challenges, the problem has received very limited attention from the research community. We propose an automated technique to localize Java Script faults based on dynamic analysis of the web application, tracing, and backward slicing of Java Script code. Our fault localization approach is implemented in an open source tool called Auto Lox. The results of our empirical evaluation indicate that (1) DOM-related errors are prominent in web applications, i.e., they form at least 79% of reported Java Script bugs, (2) our approach is capable of automatically localizing DOM-related Java Script errors with a high degree of accuracy (over 90%) and no false-positives, and (3) our approach is capable of isolating Java Script errors in a production web application, viz., Tumbler.