方法一
var str = "abcde"
str = str.split("").reverse().join("")
方法二
var str = "abcde"
var len = str.length;
var arr = str.split("")
for (var i = 0; i < parseInt(len / 2); i++) {
var temp = arr[i]
arr[i] = arr[len - i - 1]
arr[len - i - 1] = temp
}
str = arr.join("")
