Javascript ++[[]][+[]]+[+[]] === "10"

Asked Jun 11 '15 at 11:42

Active Jun 11 '15 at 11:42

Viewed 99 times

this is not a totally serious question, but I think it might help me to understand another aspect of Javascript maybe.

Some time ago, I found this strange code:

<script>
if( ++[[]][+[]]+[+[]] === "10" )
    alert( ':o');
</script>

It's actually true!

Does anyone of you know why?

asked Jun 11 '15 at 11:42

websupporter

1

I love quirky js stuff like this :) – AmmarCSE Jun 11 '15 at 11:44
1

What part of it are you having trouble with? It's just a matter of stepping through the execution path of that statement... – CodingIntrigue Jun 11 '15 at 11:45
I'm surprised to. I'd expect that expression to return an int, not a string, so with the strict `===` I'd expect false. – GolezTrol Jun 11 '15 at 11:48
1

@RGraham, Ive been stepping through. But I want to know how [Array[0]] is eventually converted to "0" -> "00" -> "10" – AmmarCSE Jun 11 '15 at 11:48
2

Oh Javascript.. You evil mistress – Pogrindis Jun 11 '15 at 11:49
I'm pretty sure this has already been asked and answered before. – Filburt Jun 11 '15 at 11:51
1

@Filburt, care to point us to an answer? – AmmarCSE Jun 11 '15 at 11:52
couldn't find it :/ but if so, please mark as duplicate and sorry. – websupporter Jun 11 '15 at 11:52
3

Not exactly the same statement but the general ideal applies: *Why is ++[[]][+[]]+[+[]] = '10'* http://stackoverflow.com/q/7202157/205233 – Filburt Jun 11 '15 at 11:54
2

@AmmarCSE : `(++[[]][+[]]) + ([+[]])` Number plus string is string. – Quentin Jun 11 '15 at 11:58
@Quentin, thanks for the explanation...that helps :) – AmmarCSE Jun 11 '15 at 12:00
I have to link this: http://escape.alf.nu/ "Why people concerned with security of their web application absolutely hate the quirky JS/HTML combo" :D Pretty soon, you'll get to using constructs like this - it's actually pretty easy to write any javascript code without using any letters or numbers - at all. – Luaan Jun 11 '15 at 13:09

Javascript ++[[]][+[]]+[+[]] === "10"

0 Answers0