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

reduce()

The reduce method reduces the collection to a single value, passing the result of each iteration into the subsequent iteration:

const collection = collect([1, 2, 3]);

const total = collection.reduce((carry, item) => carry + item);

// 6

The value for carry on the first iteration is null; however, you may specify its initial value by passing a second argument to reduce:

const total = collection.reduce((carry, item) => carry + item, 4);

// 10

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