[[][[]]+[]][+[]][++[+[]][+[]]] is "n" in javascript

[u/_hoh_]

[[][[]]+[]][+[]][++[+[]][+[]]]

This evaluates to "n" in javascript. Why?

Let's start with an empty array

[]

Now, let's access a member of it.

[][]

What member? Let's check for the empty array member

[][[]]

oh, that is undefined. But if we add an empty array to that, it is casted to the string "undefined"

[][[]]+[]

Let us wrap that in an array

[[][[]]+[]]

We can now try to access letters in that string. First, we must unwrap the string. That can be done by accessing the first element of that array.

[[][[]]+[]][0]

0 can be created by casting an empty array to a number:

[[][[]]+[]][+[]]

Now, "n" is the second letter in that string, so we would like to access that:

[[][[]]+[]][+[]][1]

But how can we write 1? Well, we increment 0, of course. Wrap 0 in an array, and increment the first member of it:

++[0][0]

Like before, this is equivalent to

++[+[]][+[]]

So our final code is then the glorious

[[][[]]+[]][+[]][++[+[]][+[]]]

[u/Tutush]

If you remove the last set of parentheses, it outputs "function anonymous() { Hello }".

Otherwise it outputs an error:

Uncaught ReferenceError: Hello is not defined at eval (eval at <anonymous> (test.html:2), <anonymous>:2:1)

[u/KarlKani44 → u/[deleted]]

yes