my-idlers/node_modules/collect.js/docs/api/duplicates.md

duplicates()

The duplicates method retrieves and returns duplicate values from the collection:

const collection = collect(['a', 'b', 'a', 'c', 'b']);

const duplicates = collection.duplicates();

duplicates.all();

// { 2: 'a', 4: 'b' }

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