Abstract: In an ECMAScript (JavaScript) Virtual Machine, applications are isolated from the operating system by defining an application context for each application. A root application context is defined that binds scripted objects of the root application context to equivalent native objects of the virtual machine. Other application contexts may send events on an event bus via the root application context to request resources of the operating system. The root application context determines the security privileges of the application context with respect to the requested resource, and is the only application context that is able to interact with the operating system.