Maps: Iteration
14.1
Convert the first book object from the books array into a Map, and assign it to a firstBookMap variable.
const firstBookMap = new Map(Object.entries(books[0]));
14.2
Use the for-of loop to iterate over firstBookMap, and log to the console keys that have numbers as values.
for (const [key, value] of firstBookMap) {
if (typeof value === 'number') console.log(key);
}