What I wish ECMAScript had was true support for number types other than the default 32-bit float. I can use 32 and 64 bit integers using "asm.js", but this introduces other complications of its own -- basically, having to program in a much lower level language.

It would be nice if EcmaScript could give us a middle ground -- ability to use 32/64 bit integers without having to go all the way down to asm.js or wasm.