QuestKit is no longer under development.
QuestKit was intended to pick up Quest 5 and become a cross-platform, JavaScript toolkit for creating text adventure games with a parser. It was abandoned some years ago, and alex subsequently left quest altogether. More on the Developer Forum.
The principle of QuestKit is being continued as QuestJS (aka Quest 6), which is under active development (as of Mar 2020!), and may ultimately adopt the name QuestKit.