第二个问题可以用这个[工具方法](https://link.segmentfault.com/?enc=O94F6AhIe5%2BVEbSEAXzlzg%3D%3D.kDRSDoTdkzB2Zde%2F9sIXLE0WPosVHwmyycAaiosCRYyZc4wEoU1WRB8iR50VE%2BLhqouSScpi0wucM81A5AL%2F8UOG%2BtouzalIGspWCLU%2F8t6Of3N8F0aTuyPPaGUv7fmK72Fpok4JiH1VWM5cBTcVkQ%3D%3D)。 第一个问题并没有复现你的问题,参考这个[demo](https://link.segmentfault.com/?enc=nWVGe4Hrvs%2BoknjXvdntlQ%3D%3D.Sg%2FUFwTMEbYs7HMATHQ5Ws00FglfpEsKQ23p7TAPDc3B2P0MW8Q0OD1QOSwUJ4is)