Cannot access array before initilaisation during swap

Ive come to something strange

Im trying to swap the array value 0 with the array value 1

Ive found a previous post stating that this is possible

[arr[0], arr[1]] = [arr[1], arr[0]];

So I wanted to replicate that

let array_names = ["Dave", "johson", "Lime", "Key", "Freeman", "Chell", "Shepart", "Furious"]
[array_names[0], array_names[1]] = [array_names[1], array_names[0]]

However something strange happens

I get an error message stating that

ReferenceError: Cannot access 'array_names' before initialization

I have checked and there isnt a typo anywhere

Also yes I did initialize the array before doing any modificiation

Your code is totally correct, but due to a missing semicolon, the interpreter parsed your code differently..

let array_names = ["Dave", "johson", "Lime", "Key", "Freeman", "Chell", "Shepart", "Furious"]
[array_names[0], array_names[1]] = [array_names[1], array_names[0]]

The expression was evaluated as

["Dave", "johson", ...][array_names[0], array_names[1]] 

The code is parsed as one line statement.

The right answer as stated by Shubhada is

let array_names = ["Dave", "johson", "Lime", "Key", "Freeman", "Chell", "Shepart", "Furious"]; //Terminate statement
[array_names[0], array_names[1]] = [array_names[1], array_names[0]];

JS is actually trying to interpret your code as :

// reduced for brevity
let array_names = ["Dave", "johson"][array_names[0], array_names[1]] = [array_names[1], array_names[0]]

It's trying to access the index [array_names[0], array_names[1]] of the array ["Dave", "johson"] and at that time, array_names not yet defined.

You can (should) use semicolon to fix that :

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let array_names = ["Dave", "johson", "Lime", "Key", "Freeman", "Chell", "Shepart", "Furious"];
[array_names[0], array_names[1]] = [array_names[1], array_names[0]];
console.log(array_names);

<!-- end snippet -->

I try following

let array_names = [
  "Dave", "johson",
  "Lime", "Key",
  "Freeman", "Chell", 
  "Shepart", "Furious"
]

console.log(array_names)

array_names[0], array_names[1] = array_names[1], array_names[0]

console.log(array_names)

temp = array_names[0]
array_names[0] = array_names[1]
array_names[1] = temp

console.log(array_names)

and get the result

[
  'Dave',    'johson',
  'Lime',    'Key',
  'Freeman', 'Chell',
  'Shepart', 'Furious'
]
[
  'Dave',    'johson',
  'Lime',    'Key',
  'Freeman', 'Chell',
  'Shepart', 'Furious'
]
[
  'johson',  'Dave',
  'Lime',    'Key',
  'Freeman', 'Chell',
  'Shepart', 'Furious'
]

as in here. But with your code I obtain

[
  'Dave',    'johson',
  'Lime',    'Key',
  'Freeman', 'Chell',
  'Shepart', 'Furious'
]
[
  'Dave',    'johson',
  'Lime',    'Key',
  'Freeman', 'Chell',
  'Shepart', 'Furious'
]

where the elements are not swapped. I do not understand either.