[_0w8t]

This describes 32 bit CPU. As opposite to V8, SpiderMonkey, Mozilla’s JS engine, uses 64 bit words and NaN boxing, even on a 32 bit CPU, to represent a generic JS thing.

[esprehn]

I'm pretty sure even on 64bit v8 doesn't use NaN boxing. Do you have docs or code that show it does?

Yes other engines use NaN boxing, but not all engines do.