I stumbled across this the other day on reddit. The poster noted that
{} + ""
is equal to 0, while the similar
"" + {}
is equal to an empty [object Object].
Normal math rules tell me this is odd, but why is it this way?
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hiybbprqag
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Because that's how the language is specified. – Ingo Bürk Jun 01 '16 at 18:44
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Also, relevant video you should watch: [wat](https://www.destroyallsoftware.com/talks/wat) – Ingo Bürk Jun 01 '16 at 18:44
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2I wish it were easier to search for duplicates of this. – Pointy Jun 01 '16 at 18:46
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1@Pointy https://stackoverflow.com/questions/22418721/1-1-and-1-object-object1-whats-going-on-there? – Bergi Jun 01 '16 at 18:50
1 Answers
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The token { at the beginning of a statement might mean the start of an object literal, or it might mean the start of a statement block. JavaScript assumes it's the latter, a statement block.
Thus
{} + ""
is just an empty statement block followed by the expression + "", which will be interpreted as 0 due to the semantics of the unary + operator.
In the other one, {} is not at the beginning of a statement, so it's unambiguously an (empty) object literal.
Pointy
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Elect me president and I'll make it a law that anybody who talks about JavaScript "wat" stuff has to offer a complete explanation of every single thing. – Pointy Jun 01 '16 at 18:50
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2I'll elect you president if you immediately ban anybody who posts "wat" questions. – Jeremy Jun 01 '16 at 18:52