How can you use regular expressions to validate HTML forms?

Regular Expressions are the most powerful tool to any textual processing in any languages. In form, this can be used to validate email addresses, address and phone number and any other data that has a very specific structure. HTML Form has a support attribute "pattern" where you can include RegEx you want to use to validate the field. This can be included such as: <input type="text" pattern="[A-Za-z0-9]{10}" id="field" name="field"> which would allow any text with a to z (or uppercase) or with numbers limit being maximum of 10 characters. Knowing RegEx is basic requirement of any coder. It can be used both in Frontend and in Backend and can provide easy solution to even most difficult parsing problem. RegEx are THE knowledge.

Regular expressions (regex) ensure that HTML form inputs match specific patterns: - Email: Validate using patterns that require characters before and after the "@" symbol, followed by a domain suffix. - Phone Numbers: Regex can validate various formats, such as (XXX) XXX-XXXX. - Passwords: Ensure criteria like uppercase, numbers, or symbols are met. - URLs: Check for prefixes like "https://" or "https://", followed by domain structures. - Dates: Validate against common formats like MM/DD/YYYY. - Feedback: On validation failure, prompt users with the required format. - Security: While regex aids user experience, always perform server-side validation too, preventing malicious data submissions.

There are some slight variations in defining RegExes depending on the language you use. For the HTML pattern attribute, you'll want to make sure to use JavaScript style Regular Expressions (which differ from PHP RegExes, for example). Further, if adding validation via JavaScript, you'll want to make sure you take the pattern attribute into account. HTML validation happens separately from any scripting you write.

Password validation has become a standard practice that encourages data protection and security. Mostly done by front-end developers. The use of regex or regular expression to validate passwords is a good start to help in compliance with policies and procedures. However, regex should be used cautiously. For example, you might want to restrict character repetition or allow character repetition. This will require that you make some changes to your regex. An example scenario below; You have a variable called x, as so; const x = ^(?!.*\s)(?=.*\d)(?=.*\p{Ll})(?=.*\p{Lu})(?=.*[!@#$%^&*]).{8,}$ This regex allows for repeated characters in the password. Choosing whether or not to allow repeated characters depends on your project requirements.

Many projects start as local products for the natives before they scale up to international regions and perform their functions. In such cases, you may want to restrict phone numbers that are submitted in your to your region. For example, if you have a product that can deal with the Kenyan shilling currency at the moment, you may want to apply phone number validations that allow numbers that start with common formats such as +254--, or 07--. You can add the regex pattern to the pattern attribute of the input field in the HTML form. For example; <input type="tel" name="phone" pattern="^(+254|0)([17][0-9]|[1][0-1]){1}[0-9]{1}[0-9]{6}$" required> This way, you can focus on strategies to scale up your application.

While client-side validation enhances UX, it shouldn't be the sole strategy. Here are 3 reasons why server-side validation is crucial, with more to consider: 1. Security: Client-side validation can be bypassed by users, risking code manipulation or direct server requests outside the UI. 2. Data Integrity: Sole reliance on client-side validation assumes all data is trustworthy. Attackers can forge requests or tamper with data before it reaches the server. Server-side validation validates data at its source, preventing malicious or incorrect input. 3. Complex Logic: Handling complex data validation and business rules requires server-side processing, beyond the capability of client-side code.