Undefined can be defined
> var t
< undefined
> t == undefined
< true // Ok, that makes sense
> t = "Defined"
< "Defined" // Ok...
> var t
< undefined // ... so far, so good...
> t == undefined
< false // ... What now?
> var t
< undefined
> t == undefined
< true // Ok, that makes sense
> t = "Defined"
< "Defined" // Ok...
> var t
< undefined // ... so far, so good...
> t == undefined
< false // ... What now?