[SOLVED] Why does optional-chaining multiple property accesses throw for an empty object, but not for null?

Why does optional-chaining multiple property accesses throw for an empty object, but not for null?

in a node repl or browser console:

> ({})?.a
undefined
> (null)?.a
undefined
> (null)?.a.b
undefined
> ({})?.a.b
Uncaught TypeError: Cannot read properties of undefined (reading 'b')

if (anything)?.a is undefined then why does the undefined that (null)?.a evaluates to NOT throw an error when I read its non-existent properties?

Solution

why does the undefined that (null)?.a evaluates to NOT throw an error when I read its non-existent properties?

It would:

> (null?.a).b
Uncaught TypeError: Cannot read properties of undefined (reading 'b')
> const temp = null?.a;
> temp.b
Uncaught TypeError: Cannot read properties of undefined (reading 'b')

The difference from that to null?.a.b is that the optional chaining operator short-circuits the entire property access (and method call) chain, stopping evaluation and just returning undefined.