var VS let VS const

	scope(범위)	value(값)
ver	globally-scoped variables	변경 가능
let	block-scoped local variables	변경 가능
cost	block-scoped local variables	변경 불가

 

var x = 1;

if (x === 1) {
  var x = 2;

  console.log(x);
  // Expected output: 2
}

console.log(x);
// Expected output: 2

 

let x = 1;

if (x === 1) {
  let x = 2;

  console.log(x);
  // Expected output: 2
}

console.log(x);
// Expected output: 1

 

const number = 42;

try {
  number = 99;
} catch (err) {
  console.log(err);
  // Expected output: TypeError: invalid assignment to const `number'
  // (Note: the exact output may be browser-dependent)
}

console.log(number);
// Expected output: 42