https://www.cnblogs.com/le220/p/9756881.html
https://blog.csdn.net/hyb1234hi/article/details/84142721
https://www.jb51.net/article/134067.htm
https://segmentfault.com/q/1010000015323261/a-1020000015323671
經典保留兩位小數：(Math.round(5.1699 * 100)/100).toFixed(2)