##Map##
A Map is a key-value collection introduced in ES6. It kind of fills the gap between arrays (no key-value pairs) and objects (key-value pairs but much more complex than a simple collection). You can create a Map like this:
let cardAce = { name: 'Ace of Spades' };
let cardKing = { name: 'King of Clubs' };
let deck = new Map();
deck.set('as', cardAce);
deck.set('kc', cardKing);
You can get values from a map by using the get(key) method. Of course you also have methods to clear a map or delete single items. Some handy methods to use on Maps are:
let contacts = new Map()
contacts.set('Jessie', {phone: "213-555-1234", address: "123 N 1st Ave"})
contacts.has('Jessie') // true
contacts.get('Hilary') // undefined
contacts.set('Hilary', {phone: "617-555-4321", address: "321 S 2nd St"})
contacts.get('Jessie') // {phone: "213-555-1234", address: "123 N 1st Ave"}
contacts.delete('Raymond') // false
contacts.delete('Jessie') // true
console.log(contacts.size) // 1
###Iterating through a Map###
let myMap = new Map()
myMap.set(0, 'zero')
myMap.set(1, 'one')
for (const [key, value] of myMap) {
console.log(key + ' = ' + value)
}
// 0 = zero
// 1 = one
for (const key of myMap.keys()) {
console.log(key)
}
// 0
// 1
for (const value of myMap.values()) {
console.log(value)
}
// zero
// one
for (const [key, value] of myMap.entries()) {
console.log(key + ' = ' + value)
}
// 0 = zero
// 1 = one
// Using the forEach method
myMap.forEach(function(value, key) {
console.log(key + ' = ' + value)
})
// 0 = zero
// 1 = one
##Set##
A Set is a collection which only holds values. Sounds like an Array? Almost, but a Set will only old unique values. That means, no value can appear more often than once in a Set. You can loop through a set to retrieve the values (or use an Iterator).
Remember, each value is unique, therefore you don’t need a key or index to delete a value! You can create a Set like this:
let cardAce = { name: 'Ace of Spades' };
let cardKing = { name: 'King of Clubs' };
let deck = new Set();
deck.add(cardAce);
deck.add(cardKing);
deck.add(cardKing); // Won’t be added, only added once!
Some basic methods available on Set are:
let mySet1 = new Set()
mySet1.add(1) // Set [ 1 ]
mySet1.add(5) // Set [ 1, 5 ]
mySet1.add(5) // Set [ 1, 5 ]
mySet1.add('some text') // Set [ 1, 5, 'some text' ]
const o = {a: 1, b: 2}
mySet1.add(o)
mySet1.add({a: 1, b: 2}) // o is referencing a different object, so this is okay
mySet1.has(1) // true
mySet1.has(3) // false, since 3 has not been added to the set
mySet1.has(5) // true
mySet1.has(Math.sqrt(25)) // true
mySet1.has('Some Text'.toLowerCase()) // true
mySet1.has(o) // true
mySet1.size // 5
mySet1.delete(5) // removes 5 from the set
mySet1.has(5) // false, 5 has been removed
mySet1.size // 4, since we just removed one value
console.log(mySet1)
// logs Set(4) [ 1, "some text", {…}, {…} ] in Firefox
// logs Set(4) { 1, "some text", {…}, {…} } in Chrome
Iterating through a Set
// iterate over items in set
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1) console.log(item)
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1.keys()) console.log(item)
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1.values()) console.log(item)
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
// (key and value are the same here)
for (let [key, value] of mySet1.entries()) console.log(key)
// using the forEach
mySet1.forEach(function(value) {
console.log(value)
})