DOM DocumentFragment对象之于性能优化的作用
https://blog.csdn.net/ai_u20/article/details/85159415
关于内存泄露
https://www.cnblogs.com/onepixel/p/8832776.html
http://jinlong.github.io/2016/05/01/4-Types-of-Memory-Leaks-in-JavaScript-and-How-to-Get-Rid-Of-Them/（避免内存泄露，写代码是应该注意的问题）
