1 and 2 I know because of work since null and undefined can be a pain when testing.
3 is string concatination with 2 being made a string to make it magically work.
4 is making the string a number to make the math operator magically work.
5 is similar to 3 in that it's concatinating an (empty) string with a number that magically becomes a string.
6 is fun because + is the shorthand for type converting to an int.
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