Currently the onChange on react-codemirror is:

onChange?: (instance: CodeMirror.Editor, change: CodeMirror.EditorChangeLinkedList[]) => void;

However, when logging the parameter change I get:

"{"from":{"line":1,"ch":12,"sticky":null,"xRel":1,"outside":1},"to":{"line":1,"ch":12,"sticky":null,"xRel":1,"outside":1},"text":["a"],"removed":[""],"origin":"+input"} 

Which make sense since it its a linked list. The type for the parameter change should simply be CodeMirror.EditorChangeLinkedList.