[Tloewald]

Well ; produces 8307 chars on its own (without eval checked) -- which seems kind of inefficient (for such a common character in idiomatic javascript). Looking that their encoder, ';' actually has a specific encoding (which itself has to be encoded) so it looks like there's some inefficient expansion taking place (e.g. '.' has a specified encoding that does not require recursive encoding). Encoding the string "link" in the expansion of ';' appears to be very expensive -- alert is cheap in comparison because you can obtain its letters from Javascript return values (e.g. "l" is pulled out of "false" which is obtained by (![]+"")[2])

I'd imagine that if you were serious about this, you'd implement, say, e=String.fromCharCode (12k chars) and use that to dig yourself out of a lot of this expensive stuff if you need more than one hard-to-encode character.