let vs const vs var

for(let i = 0; i < 5; i++){
  console.log(i);
  //0
  //1
  //2
  //3
  //4
}
console.log(i); //ReferenceError: i is not defined



for(var i = 0; i < 5; i++){
  console.log(i);
  //0
  //1
  //2
  //3
  //4
}
console.log(i); //5

//var은 블록스코프를 무시하고 변수에 접근함