Es 6文字列テンプレート相互変換

1、配列を文字列join()に変換する

let arr=["a","r","r"];
let string = arr.join(',');
console.log(typeof(string))//String
console.log(typeof(string),string)//"a,r,r"

2、文字列を配列split()に変換する

let string = 's,t,r,i,n,g';
let arr = string.split(',')
console.log(typeof(arr))//Array
console.log(arr)//["s","t","r","i","n","g"]