should be reserved undefined, NaN, Infinity

typeof "hello" → "string"

typeof 10 → "number"

typeof true → "boolean"

typeof { name : 'John' } → "object"

typeof [ 1, 2, 3 ] → "object"

Template Literals super-powered strings

She said, "It's Me!"

const name = Siri; >> Hello ${ name }!; → 'Hello Siri!'

const uniqueID = Symbol('this is a uniqueID');

typeof uniqueID → "symbol"

Only 9 values are always false and these are known as falsy values:

• "" // double quoted empty string literal
• '' // single quoted empty string literal
• `` // empty template literal
• 0
• -0 // considered different to 0 by JavaScript!
• NaN
• false
• null
• undefined

Boolean(0); → false

!!(0) → false

https://www.sitepoint.com/quick-tip-create-manipulate-arrays-in-javascript/

const letters = new Set('Hello');

letters → Set(4) [ "H", "e", "l", "o" ]

const words = new Set().add('the').add('quick').add('white').add('fox');

words → Set(4) [ "the", "quick", "white", "fox" ]

const arrays = new Set().add([1]).add([1]);

arrays → Set [ (1) […], (1) […] ]

Set(2) size: 2 entries: 0: Array [ … ] 1: Array [ … ]

const mixedTypes = new Set().add(2).add('2');

mixedTypes → Set [ 2, "2" ]

mixedTypes.size → 2

mixedTypes.has('2'); → true​

mixedTypes.delete('2') → true​

mixedTypes → Set [ 2 ]

mixedTypes.clear()

mixedTypes → Set []

spread operator with Set

const messagesShop = new Set().add('carrots').add('broccoli').add('rice');

const messagesArray = [...messagesShop];

messagesArray → Array(3) [ "carrots", "broccoli", "rice" ];

var fruits = ['Banana', 'Orange', 'Lemon', 'Apple', 'Mango'];

var citrus = fruits.slice(1, 3);

citrus → Array [ "Orange", "Lemon" ]

The keyword this refers to the object that it is within.

DOM

const body = document.body

typeof body => "object"

body.nodeType; 1

document.querySelector('#bats');

document.querySelectorAll('.hero'); NodeList(3) [ li.hero, li#bats.vigilante.hero, li.hero ]

js-novice-ninja quiz

Node v7.10.0

Node.js - REPL Terminal

developer mozilla Map

developer mozilla Object

developer mozilla Map values

hackernoon es6 maps

Interface HTMLCollection

The DOM also specifies a NodeList interface