浏览器一帧里都做了什么 nexttick

https://www.qinguanghui.com/react/%E6%B5%8F%E8%A7%88%E5%99%A8%E4%B8%80%E5%B8%A7%E9%87%8C%E5%81%9A%E4%BA%86%E4%BB%80%E4%B9%88.html#%E4%B8%80%E5%B8%A7%E9%87%8C%E4%BA%8B%E4%BB%B6%E6%89%A7%E8%A1%8C%E9%A1%BA%E5%BA%8F

vue 中nextTick保证dom更新，但不能保证渲染完成。