In JavaScript, why do []+[] return empty string, []+{} return Object, {}+[] return 0, and {}+{} return NaN?

Asked Feb 22 '12 at 17:22

Active Jun 29 '12 at 07:18

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Can anyone explain these bizarre Javascript behaviours mentioned in the 'Wat' talk for CodeMash 2012?

Someone I know gave me these examples as a reason why he can't consider javascript a proper programming language, or something along the line.

I was wondering if there are some reasons for these return values?

For the first one, I guess an explanation could be, that []=="" returns true? And therefore []+[] is 'equivalent' to ""+""? But if that's right, since []==0 returns true too, why is the empty string interpretation chosen over 0?

edited May 23 '17 at 09:59

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asked Feb 22 '12 at 17:22

Alex

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See http://stackoverflow.com/questions/9032856/can-anyone-explain-these-bizarre-javascript-behaviours-mentioned-in-the-wat-ta – anddoutoi Feb 22 '12 at 17:24
Not something, its like Duplicate² – jAndy Feb 22 '12 at 17:24
I believe he's been watching this talk: https://www.destroyallsoftware.com/talks/wat – Ptival Feb 22 '12 at 17:25
Actually, `[]+{}` returns **string** with the content of `"[object Object]"`. – duri Feb 22 '12 at 17:25
Oh, you're right. Must admit I did not search prior to posting... – Alex Feb 22 '12 at 17:27

In JavaScript, why do []+[] return empty string, []+{} return Object, {}+[] return 0, and {}+{} return NaN?

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