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@Carson63000 Declare a UInt32Array or similar. The entries are 32-bit unsigned ints declared at compile time. This is pretty much how asm.js deals with memory... and yes, I know, it's all hinky.
All depends on what the guy is doing. I would expect something like this approach to be used either if the code is running on a server where performance matters, or if this is part of a commercial product. The existing Excel-reading libraries would be a good starting point, either whole or as the basis for a bit of cannibalism :)
@Songo: Liskov means that that what works on the superclass should work on subclasses, not that things that don't work on the superclass have to also fail on subclasses. Subclasses implement additional features all the time, that's one of the main reasons we bother to write them.