?? only coalesces nullish values (hence the name), which only includes null and undefined. || coalesces falsey values, which include false, 0, and empty strings

?? only coalesces nullish values (hence the name), which only includes null and undefined. || coalesces falsey values, which include false, 0, and empty strings. || might work most of the time, but it requires extra checks when falsey values are valid.