Maps

JavaScript also offers (as of recently) support for maps: collections of key-value pairs. Map keys are unique, so adding a key that already exists will replace its value. You can set and delete entries dynamically:

const map = new Map();
map.set("bertholdt", "shifter");
map.set("reiner", "warrior");
map.set("annie", "shifter");
map.set("bertholdt", "colossal titan");
console.log(map);
// Map { 'bertholdt' => 'colossal titan', 'reiner' => 'warrior', 'annie' => 'shifter' }

map.delete("annie");
console.log(map);
// Map { 'bertholdt' => 'colossal titan', 'reiner' => 'warrior' }

Maps can be constructed from any iterable. Maps are iterable, so that means the Map constructor can accept a map:

const originalMap = new Map();
originalMap.set("bertholdt", "shifter");
const mapCopy = new Map(originalMap);
console.log(mapCopy);
// Map { 'bertholdt' => 'shifter' }

Assignment

Textio is building a phone directory for its support team. Complete the addToPhonebook function. It takes a phoneNumber and name strings, and phoneBook map as inputs and returns a new map.

Create a copy of the input phoneBook.
Add the input phoneNumber as the key to the map, with the value name.
Return the resulting Map.