这个js for 循环有什么问题么

Question

如下代码所示：

  var str = 'agsjdj23bsnqk2ndxn2dnd87hsj9n1ms29010ssh22isn1m2ms';
  var data1 = [];
  console.log(str.length);
  for (var i = 0; i < str.length; i+2) {
    // data1 = data1.concat(str.slice(i,i+2));
    // console.log(str.slice(i,i+2));
    console.log(i);
  }
  console.log(data1);

Answer 1

for (var i = 0; i < str.length; i+=2)

Answer 2

i+2什么意思？