block-variables.js

if ( condition ) {
  let x = 1;
  const y = 2;
  var z = 3;
  
  x = 4;
  y = 5;
  z = 6;
  
  console.log( x ); // 4
  console.log( y ); // 2
  console.log( z ); // 6
}

console.log( x ); // x is undeclared
console.log( y ); // y is undeclared
console.log( z ); // 6