数组里的字符串转换成数字或者把数字转换成字符串
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
arr.map(String); //结果： ['1', '2', '3', '4', '5', '6', '7', '8', '9']var a = ['1', '2', '3', '4', '5', '6', '7', '8', '9']
a.map(Number); //结果：[1, 2, 3, 4, 5, 6, 7, 8, 9]
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
arr.map(String); //结果： ['1', '2', '3', '4', '5', '6', '7', '8', '9']var a = ['1', '2', '3', '4', '5', '6', '7', '8', '9']
a.map(Number); //结果：[1, 2, 3, 4, 5, 6, 7, 8, 9]