js 用指定符号将数组转换成字符串

字符串转数组：

var str = "aa,bb,cc";

var arr = str.split(","); //["aa","bb","cc"]

数组转字符串：

var arr = ["aa","bb","cc"];

var stra = arr.toString(); //"aa,bb,cc"

var strb = arr.join(":"); //"aa:bb:cc"