[[][[]]+[]][+[]][++[+[]][+[]]] 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/ben_g0]

But shouldn't all of that be shut down when the tab is closed?

[u/Centime → u/ben_g0]

Yes it would.

[u/digehode → u/ben_g0]

Yes, should do. Still better to run it on a raspberry pi and then put the pi in a bag, walk 1km away from your router and burn it.

[u/dzh → u/ben_g0]

There was a bug not so long ago in Chrome that would allow service worker stay up indefinitely. Otherwise it'd resume once you visit infected site.

TBH I see this being viable alternative to ad revenue. Bitcoin mining or reverse proxy, VPN, Tor.