NovoManu

const symbol1 = Symbol()
const symbol2 = Symbol('id')
const symbol3 = Symbol('id')

// Each symbol is unique
console.log(symbol2 !== symbol3)

// Symbols could be used as object keys
const obj = {
  [symbol1]: 'War',

NovoManu

const target = {}
// Create proxy with no interceptors
const proxy = new Proxy(target, {})

proxy.test = 5

console.log(target.test) // Expected output: 5
console.log(proxy.test) // Expected output: 5

const arr = [1, 2, 3]

NovoManu

const promise = (duration = 0) => {
    return new Promise((resolve, reject) => {
        setTimeout(resolve, duration)
    })
}

promise(1000)
  .then(() => {
    console.log('1 sec')
    return promise(500)

NovoManu

// String methods
const str = 'my string'
console.log(str.repeat(2)) // Expected output: my stringmy string,

console.log(str.startsWith('my')) // Expected output: true
console.log(str.startsWith('st')) // Expected output: false
console.log(str.startsWith('my', 1)) // Expected output: false

console.log(str.endsWith('ing')) // Expected output: true
console.log(str.endsWith('st')) // Expected output: false

NovoManu

// lib.js
export const PI = Math.PI
const sum = (a, b) => a + b
export default sum

// file.js
import sum, { PI } from 'lib.js'
console.log(sum(1, PI)) // Expected output: 4.141592654

// lib2.js

NovoManu

function* generateSequence(start, end) {
  for (let i = start; i <= end; i++) yield i
}

const sequence1 = generateSequence(1, 10)

for (const n of sequence1) {
  console.log(n) // Expected output: sequence from 1 to 10
}

NovoManu

const fibonacci = {
  // Iterated objects must implement [Symbol.iterator] method
  // which returns object with next method
  [Symbol.iterator]() {
    let pre = 0, cur = 1
    return {
      next() {
        [pre, cur] = [cur, pre + cur]
        return { done: false, value: cur }
      }

NovoManu

// Set - collection with unique values
const set = new Set()
const john = 'John'
const diana = 'Diana'
const kate = 'Kate'

set.add(john)
set.add(diana)
set.add(kate)

NovoManu

// Map - data structure with key-value pairs, where keys can be any type
const map = new Map()

map.set('1', 'string')
   .set(1, 'number')
   .set(true, 'boolean')

const obj = { name: 'John' }
map.set(obj, 'John')

NovoManu

class Animal {
  constructor(name) {
    this.name = name
  }
  get getName() {
    return this.name
  }
  set setName(newName) {
    this.name = newName 
  }