@b08/object-map NPM

@b08/object-map, seeded from @b08/library-seed, library type: dry

Set of methods to work with null-prototyped object as map

reasoning

Main purpose of using object as hash map is to have a fast, O(1) search for items using given key/id. \ Toolset is made of few, most frequently used functions to create and work with those maps.

Reason to use null-prototyped object (null-object from now on) is to not have properties derived from usual "Object" prototype, like "constructor". Null-object will return undefined if you request "constructor" field by indexer.

limitations

There is still that special property "__proto__" that will still return nun-undefined value.
Null-object will not survive object-spread operator or serialization - deserialization. I.e. will become regular object.

toMap

Returns null-object where keys are selected by first lambda and values are selected by second lambda. If key is encountered second time, value is overwritten.

const array = [{id: 1, name: '1'}, {id: 2, name '2'}];

const result = toMap(array, item => item.id); // {1: {id: 1, name: '1'}, 2: {id: 2, name '2'}}
const result2 = toMap(array, item => item.id, item => item.name); //{ 1: "1", 2: "2" }

toGroup

Returns null-object, each entry is a key and array of values having that key.

const array = [{id: 1, name: '1'}, {id: 2, name '2'}, {id: 1, name: '3'}];

const result = toGroup(array, item => item.id); 
  // {1: [ {id: 1, name: '1'}, {id: 1, name: '3'}] 2: [{id: 2, name '2'}]}
const result2 = toGroup(array, item => item.id, item => item.name); //{ 1: ["1", "3"], 2: ["2"] }