Multiple API calls

Currently, our app can only handle 5-digit numerical postal or zip codes from the US. A postal code such as 22201 is easy to differentiate from a city name with a simplistic conditional such as typeof search === 'string'. However, postal codes can vary widely from country to country, Great Britain being a great example with postal codes such as EC2R 6AB. Even if we had a perfect understanding of how postal codes are formatted for every country on earth, we still couldn't ensure that the user didn't fat-finger a slightly incorrect postal code. Today's sophisticated users expect web applications to be resilient toward such mistakes.

After the first edition of this book was published, I received some passionate reader feedback on their disappointment that the sample app can only support US zip codes. I've decided to implement this feature because it demonstrates the degree to which such seemingly simple requests can introduce...