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toHash
Reduces a given Array-like into a value hash (keyed data store).
Given an Iterable or Array-like structure, call Array.prototype.reduce.call()
on the provided object to step over it and return an Object, keyed by the reference value.
const toHash = (object, key) => Array.prototype.reduce.call( object, (acc, data, index) => ((acc[!key ? index : data[key]] = data), acc), {} );
toHash([4, 3, 2, 1]); // { 0: 4, 1: 3, 2: 2, 1: 1 } toHash([{ a: 'label' }], 'a'); // { label: { a: 'label' } } // A more in depth example: let users = [{ id: 1, first: 'Jon' }, { id: 2, first: 'Joe' }, { id: 3, first: 'Moe' }]; let managers = [{ manager: 1, employees: [2, 3] }]; // We use function here because we want a bindable reference, but a closure referencing the hash would work, too. managers.forEach( manager => (manager.employees = manager.employees.map(function(id) { return this[id]; }, toHash(users, 'id'))) ); managers; // [ { manager:1, employees: [ { id: 2, first: "Joe" }, { id: 3, first: "Moe" } ] } ]