Charlie Harvey

check it's type...(the fact I wrote this means it's not what you would guess)

js> var a = []+[]
undefined
js> typeof a
'string'

that's a little odd to me.
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Back to my argument that a lot of this behavior is normal js> []+{} "[object Object]"

that is really misleading, remember when I said array plus something is merging strings? > ['hi']+{} 'hi[object Object]'

what your example has actually done is printed the string notation for an object and put an empty string in front of it. That's totally normal/expected behavior.
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With this next one, it is odd but it is still expected behavior

js> true+true===2
true
js> true-true===0 
true

this isn't that surprising because you are forgetting something really important, boolean + boolean will be coerced into an int to fit your strict need for addition.

js> true+true
2
js> false+true
1

Therefore if you compare the results it will not only equal the number 2 but also be a number itself!

js>true+true === 1+1
true

I hope this helps everyone understand these oddities that aren't specific to just javascript.