It's not really a ternary operator though, because the value that is tested for existence is only evaluated once, e.g. instead of a != null ? fn(a) : null

It's not really a ternary operator though, because the value that is tested for existence is only evaluated once, e.g. instead of a != null ? fn(a) : null it's more like (a, fn) => a != null ? fn(a) : null