!!arg
Return true when arg is defined, false when undefined.
+!!arg
Same as !!arg, but returns 1 or 0.
[]+arg
Convert arg into a string.
arg|0
arg>>0
~~arg
Convert arg into an integer. (e.g. ~~-2.5 makes -2.) Important thing is dislike parseInt(null) makes NaN, null|0, null>>0 and ~~null make 0.
-~arg
Return the next number of arg. This technique is based on Two's complement.
!{}
![]
false.
!!{}
!![]
true.

Reference