The correct answer is C.
When getAvailability(item) returns true, the code inside the if block executes:
var msg = "Username available";
return msg;
The variable msg receives the string value:
"Username available"
Then that same value is returned from the function.
The key point is that var is function-scoped, not block-scoped. So msg belongs to the function scope of getAvailabilityMessage(). However, because the return msg; statement is inside the same if block, the function immediately returns the assigned string when the username is available.
Option A is incorrect because msg is defined before it is returned.
Option B is incorrect because "newUserName" is not assigned or returned anywhere in the function.
Option D would only happen if getAvailability(item) returned false, because then the function would finish without an explicit return value.
For the available username scenario, the verified answer is C.