JavaScript Scope

// Prints 3 thrice, not what we meant.
for (var i = 0; i < 3; i++) {
  setTimeout(\_ => console.log(i), 10);
}

// Prints 0, 1 and 2, as expected.
for (let j = 0; j < 3; j++) { 
  setTimeout(\_ => console.log(j), 10);
}

The variable has its own copy using let, and the variable has shared copy using var.

for (let i = 0; i < 3; i++) {
  // This is the Max Scope for 'let'
  // i accessible ✔️
}
// i not accessible ❌

for (var i = 0; i < 3; i++) {
  // i accessible ✔️
}
// i accessible ✔️

var is scoped to the nearest function block, and let is scoped to the nearest enclosing block.

// Variable declared globally
const color = 'blue';
function printColor() {
  console.log(color);
}
printColor(); // => blue

const isLoggedIn = true;
if (isLoggedIn == true) {
  const statusMessage = 'Logged in.';
}
// Uncaught ReferenceError...
console.log(statusMessage);

function myFunction() {

  var pizzaName = "Margarita";
  // Code here can use pizzaName

}
// Code here can't use pizzaName