> a = { b : {} };

> f = a["b"]["c"]["d"]["e"]
  Uncaught TypeError: Cannot read properties of undefined (reading 'd')
    at <anonymous>:1:16

> f = a.b.c.d.e
  Uncaught TypeError: Cannot read properties of undefined (reading 'd')
    at <anonymous>:1:11

##</code><code>##

> a["b"]["c"]["d"]["e"] ="X"
  Uncaught TypeError: Cannot read properties of undefined (reading 'd')
    at <anonymous>:1:12

> a.b.c.d.e = "X"

 Uncaught TypeError: Cannot read properties of undefined (reading 'd')
    at <anonymous>:1:7


##</code><code>##

> perl -de0
...
  DB<1> $a->{b}{c}{d}="X"

  DB<2> x $a
0  HASH(0x32445c8)
   'b' => HASH(0x3244220)
      'c' => HASH(0x3244130)
         'd' => 'X'
  DB<3>