30-seconds-of-code/snippets/toHash.md

toHash

Reduces a given Array Like into a value hash(keyed data store)

Given an Iterable or Array like structure we 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" } ] } ]