Set and Map were introduced in ES6 as new features.
Set
Similar to array-like. It enforces uniqueness for each item inside this Set and keeps the order of the inserted items no matter what.
Set methods
add() - Adds new item delete() - removes new item has() - checks if item exists clear() - clears the set forEach() - loops through items entries/values - returns new iterator object
Set in action
//
const animals = new Set();
animals.add('monkey');
animals.add('rhino');
animals.add('rhino');
animals.forEach((item) => {
console.log(item); //monkey //rhino
});
animals.delete('rhino'); //deletes rhino item
console.log(animals.has('monkey')); //return true
animals.clear(); //clears the set
//
Each item in the Set should be unique so we cannot add two identical values to our Set.
Map
A list of key values pairs, enforce uniqueness. Keeps the order of the inserted items no matter what. Differences between a normal object and a Map can be any data. In object keys will be always converted to strings.
Map methods
get(key) - return the item value set(key, value) - adds new key-value pair delete(key) - removes the item has(key) - checks if item exists forEach() - loops through items clear() - clears the entire map entries/keys/values - returns new iterator object
Map in action
//
const animals = new Map();
animals.set('shark', 'dangerous animal');
animals.set('dog', 'friendly animal');
animals.forEach((value, key) => {
console.log(`${key} = ${value};`); //shark = dangerous animal; dog = friendly animal;
});
animals.delete('shark');
console.log(animals.has('shark')); //false, because we just deleted it
console.log(animals.get('dog')); // friendly animal
animals.clear(); //clears the map
//
Summary
Set and Maps give us a good opportunity to use them for simple or even complex data structures, where the use of objects or arrays can be problematic.