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[...a, ...b] combines arrays; {...a, ...b} merges objects.

What does [...xs, 4] do?

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const xs=[1,2];
console.log([...xs,3].join(','));

JavaScript 1 automatic check Working with data

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const xs=[1,2];
console.log([...xs,3].join(','));

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const xs=[1,2];
console.log([...xs,3].join(','));

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