improve types

src/editor/offset.ts

@@ -15,16 +15,17 @@ limitations under the License.
 */
 
 import EditorModel from "./model";
+import DocumentPosition from "./position";
 
 export default class DocumentOffset {
     constructor(public offset: number, public readonly atNodeEnd: boolean) {
     }
 
-    asPosition(model: EditorModel) {
+    public asPosition(model: EditorModel): DocumentPosition {
         return model.positionForOffset(this.offset, this.atNodeEnd);
     }
 
-    add(delta: number, atNodeEnd = false) {
+    public add(delta: number, atNodeEnd = false): DocumentOffset {
         return new DocumentOffset(this.offset + delta, atNodeEnd);
     }
 }