Hey @xuncanzhe1, thanks for the question!
It just so happens that we are currently rebuilding and upgrading Sandcastle! One of the changes is to treat the JS code in a sandcastle as a type="module"
script so import statements work, both from CesiumJS and external scripts. Feel free to read more or leave feedback in this thread: Upgrading Sandcastle: We Need Your Input!
That said, you should have full access to everything Cesium exports in the global Cesium
object in Sandcastle. Can you share more about what you’re not able to access? Or explain more what specific problems you’re running into using Sandcastle?