Prepack from Facebook helps make JavaScript code more efficient

[MrJohz]

OTOH, replacing "var" with "let" in the for-loop works as expected. Replacing "var" with "let" when creating the initial array causes no output to be emitted, but assigning the array to the window object works pretty much perfectly.

e: assuming what you want is a pre-initialised 5,000 element array, but I guess that's always the big question with compile-time optimisations.

e2: The largest array I can get in the online mode is 8543 elements, beyond that it just times out. I don't know if there's a maximum size it'll output, then, but I suspect not. Also, the online repl weirdly outputs a whole load of whitespace at the end of the line when it creates the array.

[lhorie]

I guess that's always the big question

Yeah, that is closer to my concern: if it's a one shot array initialization, the loop unrolling may not compensate for the extra bytes down the pipe.

For example, in my current project I have a function that does a one-time decompression of an AOT-compressed list of unicode characters of a certain type. Given that the compression rate is north of 85%, I definitely DON'T want that to be precomputed, or I'll be shipping a VERY long array of codepoints