Hoisting

example.js

// Antipattern:

var x = 10;

var y = function () {
  console.log(x); // logs undefined
  var x = 20;
  return x + 10;
};

// Good pattern:

var x = 10;

var y = function() {
  var x = 20;
  console.log(window.x);
  return x + 10;
};