@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

1. There is still that special property "__proto__" that will still return nun-undefined value.
2. 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"] }

keys and values

keys and values return all keys and values respectively, support both regular object and null-object.

get and has

By given key, get and has return value and presence indicator respectively, support both regular object and null-object.

toEs6Map

Converts object to ES6 Map with the same keys and values. As the name implies.

forIn

Iterates over object entries. Use for optimization purposes only. Otherwise just iterate over keys.