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JavaScript (sh.itjust.works)
submitted 1 week ago by sjmarf@sh.itjust.works to c/programmer_humor@programming.dev
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[-] victorz@lemmy.world 38 points 1 week ago* (last edited 1 week ago)

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.

[-] PoolloverNathan@programming.dev 43 points 1 week ago* (last edited 1 week ago)

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:

[-] victorz@lemmy.world 20 points 1 week ago

So there's yet another level of quirkery to this bullshit then, it seems. ๐Ÿ˜† Nice digging! ๐Ÿค

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

> eval('{} + []')
0
> eval('({}) + []')
'[object Object]'
[-] PoolloverNathan@programming.dev 10 points 1 week ago

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

[-] dejected_warp_core@lemmy.world 3 points 1 week ago

/me goes back to get second folding chair.

[-] victorz@lemmy.world 1 points 1 week ago* (last edited 1 week 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.

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this post was submitted on 23 Jun 2024
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