OK, I was reading an article on optimising JS for Googles V8 engine, when i saw this code example...

I nearly skimmed over it, but then I saw this; |=; a[0] |= b;

a = new Array();
a[0] = 0;
for (var b = 0; b < 10; b++) {
  console.log(a, b)
  a[0] |= b;  // Much better! 2x faster.
}

a[0] |= b;

So I ran it, in my console, with a console.log in the loop and resulted in 15;

[15] 0
[15] 1
[15] 2
[15] 3
[15] 4
[15] 5
[15] 6
[15] 7
[15] 8
[15] 9

WHAT?!?! Where the hell does it get 15 from, on every iteration?!?!?!

I've been a web dev for 7 years, and this has stumped me and a fellow colleague.

Can somebody talk me through this code?

Cheers.