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JavaScriptIntermediate#objects
JavaScriptIntermediate#es6#collections
Difference between Map/Set and plain objects/arrays?
Map allows any key type, keeps insertion order and exposes size with O(1) add/delete. Set stores unique values and makes deduplication trivial, whereas objects coerce keys to strings and arrays need O(n) lookups.
Example
const s = new Set([1,1,2]); // {1,2}
[...new Set(arr)]; // dedupe
const m = new Map();
m.set({id:1}, 'obj key');