// Misunderstanding scope:thinking that block-level scope exist here
var array = [];
for (var i = 0; i < 3; i++) {
  // Every 'i' in the bodies of the three arrow functions referes to the same binding,
  // which is why they all return the same value of '3' at the end of the loop.
  array.push(() => i);
}
var newArray = array.map(el => el());
console.log(newArray); // [3, 3, 3]