I'd say null/undefined is a good candidate for a falsey value since existence checking is a very common operation. Conceptually I'd rather check what the incomi

I'd say null/undefined is a good candidate for a falsey value since existence checking is a very common operation. Conceptually I'd rather check what the incoming variable is, as opposed to what it is not. Anything else is dangerous or incredibly dangerous ( e.g. 0 == false ). Besides empty variables, like [] or {} or "", are usually handled pretty well by code that works with non-empty equivalents so there's no conceptual or pragmatic reason to have those evaluate to false.