JavaScript: Why does false.something evaluate to undefined?

Question

While learning about the optional chaining operator I experimented a bit and found out that these two evaluate to undefined:

false.nonExistingProperty // undefined
true.nonExistingProperty // undefined

But why is that so? Shouldn't this throw an error?

Answer 1

When properties are accessed on primitives, JavaScript auto-boxes the value into a wrapper object and accesses the property on that object instead.

https://developer.mozilla.org/en-US/docs/Glossary/Primitive

false and true are implicitly converted to Boolean objects here, i.e. you are reading nonExistingProperty from a Boolean instead of the boolean primitive.