How to use the immer.isDraft function in immer

protected changeState(effect: Function, state: any, action: ActionResponseHandle | ActionNormalHandle): any {
    if (isDraftable(state)) {
      const draft = createDraft(state);
      const responseDraft = effect(draft, action);

      if (responseDraft === undefined) {
        state = finishDraft(draft);
      } else if (isDraft(responseDraft)) {
        state = finishDraft(responseDraft);
      } else {
        state = responseDraft;
      }
    } else {
      state = effect(state, action);

      if (state === undefined) {
        throw new StateReturnRequiredError(action.type);
      }
    }

    return state;
  }
}

parent.children.splice(index + 1, 0, newNode)

        if (selection) {
          for (const [point, key] of Range.points(selection)) {
            selection[key] = Point.transform(point, op)!
          }
        }

        break
      }
    }

    editor.children = finishDraft(editor.children) as Node[]

    if (selection) {
      editor.selection = isDraft(selection)
        ? (finishDraft(selection) as Range)
        : selection
    } else {
      editor.selection = null
    }
  },
}

parent.children.splice(index + 1, 0, newNode)

        if (selection) {
          for (const [point, key] of Range.points(selection)) {
            selection[key] = Point.transform(point, op)!
          }
        }

        break
      }
    }

    editor.children = finishDraft(editor.children) as Node[]

    if (selection) {
      editor.selection = isDraft(selection)
        ? (finishDraft(selection) as Range)
        : selection
    } else {
      editor.selection = null
    }
  },