the sign of the zeroes should not matter, but this is a known issue with the deepEqual() matcher from the chai JavaScript assertions library that Codewars uses. it uses the Object.is() function to compare objects, and Object.is(-0, +0) === false. it seems to be possible to reconfigure this in more recent (5.0+) versions of chai, but Codewars uses 4.3.3 for now.

check this out:

const xs = {};
xs[{}] = '???';
({a : 'b'}) in xs; // true

JavaScript's object-to-string conversion is messy ;-)

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