Array, string, json conversion

Array to string (comma-separated string)
var arr = new Array(3)
arr[0] = "wanggeying"
arr[1] = "John"
arr[2] = "Thomas"

console.log(arr); //arr = ["wanggeying", "John", "Thomas"]

var arrstring=arr.join(",");

console.log(arrstring);//arrstring = "wanggeying,John,Thomas"