Why does 2 == [2] in JavaScript?

I recently discovered that 2 == [2] in JavaScript. As it turns out, this quirk has a couple of interesting consequences:

var a = [0, 1, 2, 3];
a[[2]] === a[2]; // this is true

Similarly, the following works:

var a = { "abc" : 1 };
a[["abc"]] === a["abc"]; // this is also true

Even stranger still, this works as well:

[[[[[[[2]]]]]]] == 2; // this is true too! WTF?

These behaviors seem consistent across all browsers.

Any idea why this is a language feature?

Here are more insane consequences of this "feature":

[0] == false // true
if ([0]) { /* executes */ } // [0] is both true and false!

var a = [0];
a == a // true
a == !a // also true, WTF?