function createArray() {
  const storage = {};
  return {
    length: 0,
    push: (value) => { /* TODO */ },
    pop: () => { /* TODO */ }
  };
}
const myArray = createArray();
myArray.push(11);
console.log(myArray);// myArray looks like {0: 11}
myArray.push(12);
console.log(myArray); // => {0: 11, 1: 12}
myArray.length; // => returns 2
myArray.pop(); // => returns 12
myArray.length; // => returns 1