The problem is as shown in the picture,
I don’t understand why undefined is displayed in the program? The console reports an error?
伊谢尔伦2017-07-05 10:58:12
Your array only has two items, so if you get a[3], the fourth item will of course be undefined...
The same is true for the ob object. It does not have a key of 3, but only a key of 1.
