308
edits
Changes
Add a bit about nsWrapperCache
In the Web IDL case, reflectors are created by the Wrap method that the binding code generator spits out for the relevant Web IDL interface. So for the Document interface, the relevant method is mozilla::dom::Document_Binding::Wrap. The JSClass that is used is also created by the code generator, as part of the DOMJSClass struct it outputs. Web IDL objects provide a GetParentObject() method that is used to determine the right global to use for the reflector.
Web IDL objects typically inherit from nsWrapperCache, and use that class to store a pointer to their reflector and to keep it alive as needed. The only exception to that is if the Web IDL object can only cross the C++-to-JS boundary once, typically at construction time. In that case, there is no need to get the JS object from the C++ one, and no way to end up in any of the situations that require preserving the JS object from the C++ side, so the Web IDL object is allowed to not inherit from nsWrapperCache.
=== Security ===
