This isn’t quite reactive yet though. We still need some way of triggering the functions to be re-run when state changes.
However, the new device still retails for the same price of $599 for the 11-inch model, and $799 for the 13-inch model. For educational customers, the discount brings the price down to $549 for the 11-inch iPad Air, while the 13-inch model starts at $749.
，更多细节参见新收录的资料
width = progress / 4，详情可参考新收录的资料
A self-refuting example，这一点在新收录的资料中也有详细论述