How "nanundefined"[10] ="e" Or ([+[][[]]]+[][[]])[++[[]][+[]]+[+[]]] = "e"?

Possible Duplicate: Can you explain why ++[[]][+[]]+[+[]] = 10 As we all know that Cheat sheets are the shortest ways we can find to accomplish things by using the charsets. I c

Solution 1:

"NaNundefined"[10] ="e" is easy - e is the eleventh char in the string.

([+[][[]]]+[][[]])[++[[]][+[]]+[+[]]] = "e" is a bit harder, but you can easily just split it up:

[+[][[]]] -> [ NaN ]
[][[]] -> undefined
[ NaN ] + undefined -> "NaNundefined"
++[[]][+[]] -> 1
[+[]] -> "0"1 + "0" -> "10""NaNundefined"["10"] -> "e"

The second version is effectively a way to construct the first, (ab)using the weak typing of javascript operators (for example, [NaN] + "" -> "NaN"). It also uses the fact that arrays in javascript are always indexed by a string (so array[10] is equivalent to array["10"]).

The second version could be seen as a obfuscation, if you want to prevent someone to understand the code. It doesn't really serve much of a purpose though, at least in everyday coding life.

Solution 2:

The character at index 10 is an e: "NaNundefined"[10] ="e"