I am puzzled with this one. I have the following code.

```
var s = "test";
s.len = 4;
var t = s.len;

```

The question is why the variable `t` has a value of `undefined`.

If you check the `s.len` after that code it is undefined.
If you check `s` the value is `test`. Not sure what is going on here. I am sure there is an explanation, but can't get my head around that and don't know how to search that.

For those who consider to vote down. This is a question we got in a course, and we are expected to prepare for the next session with this *riddle*.
I am not new to programming, but I fail to research how JavaScripts treats this code. It is valid code really, execute it in your Dev Tools and you will see.

I define a property for the string s called len assign to it the value 4. This property is, I believe created, but undefined. I would like to now why is it ? Is it specific to strings in JavaScript ?