JavaScript: what is NaN, Object or primitive?

This is a primitive. You can check several ways:

• typeof NaN gives a "number", not an "object".

• Add a property, it disappears. NaN.foo = "hi"; console.log(NaN.foo) // undefined

• NaN instanceof Number gives false (but we know this number, so it should be primitive).

NaN , 0 / 0 NaN, . NaN , , .