數組里的字符串轉換成數字或者把數字轉換成字符串

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
arr.map(String);  //結果： ['1', '2', '3', '4', '5', '6', '7', '8', '9']

var a = ['1', '2', '3', '4', '5', '6', '7', '8', '9']
a.map(Number);  //結果：[1, 2, 3, 4, 5, 6, 7, 8, 9]

參考地址【廖雪峰的網站】：https://www.liaoxuefeng.com/wiki/001434446689867b27157e896e74d51a89c25cc8b43bdb3000/001435119854495d29b9b3d7028477a96ed74db95032675000