Review Lexical Scope

var leftEarly;
var broughtChips;
var invitedTooManyFriends;
var hadTooMuchFun;

function party(personOne, personTwo, personThree) {
    leftEarly = personOne
    broughtChips = personTwo
    invitedTooManyFriends = personThree
    var randomPerson = Math.floor(Math.random() * 3);
    var hadTooMuchFun = arguments[randomPerson];
}

party("Berto", "CJ", "Danny", "Kyle")
console.log("Left Early: ", leftEarly);
console.log("BroughtChips: ", broughtChips);
console.log("Invited Too Many Friends: ", invitedTooManyFriends);
console.log("Had Too Much Fun: ", hadTooMuchFun);

What happens when we run this?

hadTooMuchFun is undefined because it was never assigned a value

The other variables had values assigned through lexical scope

Hoisting

var berto = "He is a great guy"

makeBertoFunny()
trashTalkBerto()

console.log(berto)

function makeBertoFunny () {
    berto += " and he is super funny!"
}

var trashTalkBerto = function () {
    berto = "He is stupid and boring"
}

What happens when we run this?

TypeError!!

var berto = "He is a great guy"

makeBertoFunny()
trashTalkBerto()

console.log(berto)

function makeBertoFunny () {
    berto += " and he is super funny!"
}

var trashTalkBerto = function () {
    berto = "He is stupid and boring"
}

`trashTalkBerto` is undefined when it is invoked because it doesn't get hoisted like `makeBertoFunny`

Python Tutor

Closures

Closures are functions that refer to independent (free) variables (variables that are used locally, but defined in an enclosing scope).
In other words, these functions 'remember' the environment in which they were created.

Great for interview questions:

function writeInJournal() {
  var message = "I love alpacas"
  return readJournal
  function readJournal() {
    return "Roberto's journal says: " + message
  }
}

var read = writeInJournal();
var secret = read()
console.log(secret);