djD-REK

// let example
{ let variable = 3 } // Created in local scope (the current block scope)
console.log(variable) // ReferenceError: variable is not defined

// var example
{ var variable = 37 } // Created in global scope (the current function scope)
console.log(variable) // 37

// const example
const object = {hello: "world"} // Created in local scope (the current block scope)

djD-REK

for(let i = 0; i < 3; i++) { console.log(i) } // 0, 1, 2
console.log(i) // ReferenceError: i is not defined

djD-REK

var variable = 37
function myFunction () {
  var variable = 40
  console.log(variable) // 40
}
console.log(variable) // 37
myFunction()
console.log(variable) // 37
// Output: 37, 40, 37

djD-REK

var variable = 37
function myFunction () {
  variable = 40
  console.log(variable) // 40
}
console.log(variable) // 37
myFunction()
console.log(variable) // 40
// Output: 37, 40, 40

djD-REK

const constant = 37
console.log(constant) // 37
constant += 1 //  TypeError: invalid assignment to const `constant'

djD-REK

function myFunction () {
  console.log(variable) // 27
  variable = 40 }
console.log(variable) // undefined
variable = 27
myFunction()
console.log(variable) // 40
var variable = 37
// Output: undefined, 27, 40

djD-REK

function myFunction () {
  console.log(variable) // undefined
  var variable = 40 }
console.log(variable) // undefined
variable = 27
myFunction()
console.log(variable) // 27
var variable = 37
// Output: undefined, undefined, 27

djD-REK

let variable = 37
function multiplyBySomeNumber(number) {
  return function(innerNumber) {
     return innerNumber * number
  }
}
// equivalent to multiplyBySomeNumber = number => innerNumber => number * innerNumber
const multiplyByFive = multiplyBySomeNumber(5)
let variableTimesFive = multiplyByFive(variable)
console.log(variableTimesFive) // 185

djD-REK

// global var example
function myFunction() {
  whoops = 3
}
console.log(whoops) // ReferenceError: whoops is not defined
myFunction()
console.log(whoops) // 3

djD-REK

// global var example
function myFunction() {
  whoops = 3
}
console.log(whoops) // undefined
myFunction()
console.log(whoops) // 3
var whoops