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JavaScript (sh.itjust.works)

submitted 4 months ago by [email protected] to c/[email protected]

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[–] [email protected] 39 points 4 months ago* (last edited 4 months ago) (1 children)

In node, I get the same result in both cases. "[object Object]"

It's calling the toString() method on both of them, which in the array case is the same as calling .join(",") on the array. For an empty array, that results in an empty string added to "[object Object]" at either end in the respective case in the picture.

Not sure how we'd get 0 though. Anybody know an implementation that does that? Browsers do that maybe? Which way is spec compliant? Number([]) is 0, and I think maybe it's in the spec that the algorithm for type coercion includes an initial attempt to convert to Number before falling back to toString()? I dunno, this is all off the top of my head.

[–] [email protected] 43 points 4 months ago* (last edited 4 months ago) (1 children)

The inspector REPL evaluates as a statement-with-value (like eval), so the {} at the beginning is considered an empty block, not an object. This leaves +[], which is 0. I don't know what would make Node differ, however.

Edit: Tested it myself. It seems Node prefers evaluating this as an expression when it can, but explicitly using eval gives the inspector behavior:

[–] [email protected] 20 points 4 months ago (1 children)

So there's yet another level of quirkery to this bullshit then, it seems. 😆 Nice digging! 🤝

I also noticed that if you surround the curlies with parentheses, you get the same again:

> eval('{} + []')
0
> eval('({}) + []')
'[object Object]'

[–] [email protected] 9 points 4 months ago (2 children)

Yep, parentheses force {} to be interpreted as an expression rather than a block — same reason why IIFEs have !function instead of just function.

[–] [email protected] 3 points 4 months ago

/me goes back to get second folding chair.

[–] [email protected] 1 points 4 months ago* (last edited 4 months ago)

I thought IIFE's usually looked like (function (...params) {})(...args). That's not the latest way? To be honest I never used them much, at least not after arrow functions arrived.