Okay, so I'm actually going to explain the other, better version, but it's basically the same thing:

(![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]+!+[]+!+[]+!+[]+[]]+(![]+[])[+!+[]+!+[]+!+[]]

[Thread] 1/9 https://twitter.com/AllesHQ/status/1285538646733586432

Let's deconstruct this, it's the combination of 5 parts, 5 letters:

(![]+[])[+!+[]] = "a"
(![]+[])[!+[]+!+[]] = "l"
(![]+[])[!+[]+!+[]] = "l"
(![]+[])[+!+[]+!+[]+!+[]+!+[]+[[]]] = "e"
(![]+[])[+!+[]+!+[]+!+[]] = "s"

2/9

Each part has the same first segment:
(![]+[]). What does it mean? If we run it in a javascript console, we get "false". As in, it's a string. JavaScript's type conversion is weird, but [] is a truthy value, so if we invert it using !, it will be false. Then if we add...

3/9

[] to it, it will become a string.

Let's look at some other examples of this:

"abc" + [] = "abc"
1 + [] = "1"

Concatenating something with an empty array turns it into a string.

So (![] + []) = (false + []) = "false"

4/9

Now, have you noticed the key part yet? Alles contains the letters a, l, e and s. All of those letters are in the word false.

Since computers count from 0, if I have "false"[0], that's the first letter, "f". "false"[1] is "a", and so on.

5/9

So if we think about it, this code really means:

"false"[1] + "false"[2] + "false"[2] + "false"[4] + "false"[3]

If you run that, you get "alles". But how do we get the numbers?

"false"[1] = (![]+[])[+!+[]]

+!+[] = 1

Here's where type conversion gets even weirder

6/9

If we put + before something, it will convert it to a number. If we put ! before something, it will convert it to the opposite boolean - a truthy value to false, and a falsy value to true.

So remember how we learnt earlier that ![] is false? Well +[] is 0.

7/9

Now if we invert 0, like !0, we get true.
!+[] = true

But then we can make true a number by prepending +.
+!+[] = 1

And therefore:
+!+[]+!+[] = 2
+!+[]+!+[]+!+[] = 3
+!+[]+!+[]+!+[]+!+[] = 4

So "false"[+!+[]] = "a"

"false"[+!+[]+!+[]] = "l"

and so on.

8/9

So in conclusion

"a"
= "false"[1]
= (false + [])[1]
= (![] + [])[1]
= (![] + [])[+true]
= (![] + [])[+!false]
= (![] + [])[+!0]
= (![] + [])[+!+[]]

Then we just do that for every letter.
JavaScript is weird.
Thank you for coming to my TED talk.
9/9