Why is the variable after the ajax request set to undefined?

Question

JavaScript

Guys, I sat down to write code and came across some kind of nonsense I didn’t understand) This is probably one of the js jokes. Please explain. Declared a global empty variable. when I use it in a function, a local variable is automatically created and the values ​​are written to it, and not to the global one. How to fix it?
jsfiddle.net/iffkomc/ro3hmxpa

Answer 1

when I use it in a function, a local variable is automatically created and values ​​are written to it, and not to the global one

This is not true. Scopes have nothing to do with it, the point is asynchrony - alert is executed before the request is completed and at this moment the user data has not yet been received.
You here: How to make so that the function is executed only after the other is completed?