: Use the entered code to instantly suggest the corresponding city and country. 2. Regex Validation Rules

: Do not force a hard 5-digit limit or automatic hyphenation until the user's country is selected.

{ "input_code": "015107", "is_valid": true, "country": "China", "country_iso": "CN", "region": "Inner Mongolia", "city": "Bayannur" } Use code with caution. Copied to clipboard js backend API endpoint ?

Store postal codes as strings rather than integers to prevent the system from dropping critical leading zeros (such as the 0 in 015107 ).

To build a software feature around this specific data point, it is best to treat it as a problem.

Apply these conditional regular expression constraints depending on the detected or selected country: Code Example Regex Pattern 015107 ^[0-9]{6}$ United States 90210 ^[0-9]{5}$ United States (ZIP+4) 90210-4321 10 Characters ^[0-9]{5}-[0-9]{4}$ 3. Database Schema (PostgreSQL Example)