40 是视野角度（FOV），就像你睁大眼睛还是眯着眼睛看。
This viral animation, which began circulating widely in 2016, shows Dragonite and Charizard dancing with surprising elegance, their massive bodies moving with pop-star precision. Most people know it set to Ariana Grande's "Into You," where the contrast between her breathless vocals and their enthusiastic choreography made the clip instantly funny and weirdly perfect.，详情可参考91视频
。关于这个话题，Line官方版本下载提供了深入分析
// 易错点2：漏写stack.length判断 → 栈空时访问stack[-1]会报错
Mat Smith for Engadget，这一点在51吃瓜中也有详细论述