js如何截取中文字符串

 var str = 离线

        var arr = new Array();
        var i = 0;
        while (i 256) {
            s=s+str.charAt(i);
            i++;
          }
          arr.push(s);
        }
		for (var i = 0; i < arr.length; i++) {
          var obj = arr[i];
          console.log(obj)
        }