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JS translation kumited and if you want to approve it, I can then start to edit your kata to add a few more test cases, random test included :)

Removes nil values from the array.

I think it's fine the way it is. Requiring strings won't change the solution that much.

As alpardel said it's the left bitwise shift operator if applied to a Number

If you take an integer 11 which is 1011 in binary and shift the bits 1 to the left you get 10110 = 22
if you shift them 2 to the left you get 101100 = 44

It's a left-shift bit operator: x << n shifts the bits of 'x' n position to the left, doubling its value once for each shift. E.g.: 3 << 2 = 3 * 2 * 2 = 12

http://en.wikipedia.org/wiki/Bitwise_operation#Bit_shifts