Theseus: Understanding Asynchronous Code Tom Lieber MIT CSAIL Cambridge, MA 02139 USA tl@csail.mit.edu Figure 1: Theseus with two pseudo-breakpoints active. Copyright is held by the author/owner(s). CHI’13, April 27 – May 2, 2013, Paris, France. ACM 978-1-XXXX-XXXX-X/XX/XX. Abstract The behavior of JavaScript is difficult to understand due to the language’s asynchronous and dynamic nature. In part