Mastering Immutable.js

Filtering fancy keys

Unlike plain JavaScript objects, Immutable.js maps can use anything as a key. A common use of this capability is to associate data with a map that you don't necessarily want to add to the map as a value. You can then filter the map based on the maps used as keys:

const myFancyMap = Map.of(  Map.of('name', 'one'), 1,  Map.of('name', 'two'), 2,  Map.of('name', 'three'), 3);const myFilteredMap = myFancyMap.filter(  (v, k) => k.get('name').startsWith('t'));console.log('myFancyMap', myFancyMap.toJS());// -> myFancyMap// -> { 'Map { "name": "one" }': 1,// ->   'Map { "name": "two" }': 2,// ->   'Map { "name": "three" }': 3 }console.log('myFilteredMap', myFilteredMap.toJS());// -> myFilteredMap// -> { 'Map { "name": "two" }': 2,// -> ...