Parts of the QtScript API unfortunately reflect the implementation of the old (Qt 4.5) back-end.
This makes it difficult to implement the complete API (and behavior) on top of other JavaScript engines, such as JavaScriptCore (JSC) and V8.

Currently we are in the situation that we have to maintain our own patches on top of JSC (see QTBUG-11467) in order to fully support our API, and it will not be possible to upstream all these patches.
Therefore, we should start deprecating the relevant API, and, where applicable, propose the "right" way to do it with existing API, or introduce new API that isn't bound to a particular implementation/back-end.

In many cases, API can't be obsoleted (as in adding a qdoc \obsolete tag) until a replacement API is available. Until that happens, the deprecated API should at least be clearly marked in the docs, advising users to refrain from using it in new code.