In modern web development, user input validation is one of the most critical tasks. It ensures that the data sent to the server is clean, expected, and secure. A common and practical scenario is when you need to allow only numeric input(e.g., for phone numbers, ages, ZIP codes) or only alphabetical input (e.g., for names, surnames, cities).

While HTML5 provides some built-in tools for basic validation, they are not always sufficient or reliable for real-time input filtering—especially when it comes to preventing unwanted characters from being entered at all. … More How to Allow Only Numbers or Letters in Input Fields