validatorjs/validator.js

Validator.js is a JavaScript library that checks whether a piece of text matches a particular format and can also clean up text so it is safe to use. The problem it solves is simple: when users fill in forms on a website, you need to verify that an email address looks like an email address, a credit card number has the right structure, a date is a real date, and so on. Doing these checks from scratch is error-prone and repetitive, so validator.js provides ready-made functions for all of them. The library works entirely with strings, plain text, rather than numbers, dates, or other types. You call a function like isEmail, isCreditCard, isURL, or isPostalCode, pass in the text you want to check, and get back true or false. There are over a hundred such validators covering everything from IP addresses and ISBN numbers to Bitcoin wallet addresses and IBAN bank codes. Many accept locale options, so for example isAlpha can check that a string contains only letters according to the rules of Arabic, Japanese, German, or dozens of other languages. Alongside validation, the library offers sanitizer functions that strip or escape dangerous characters from user input before storing it in a database or displaying it on a page, helping prevent security problems like cross-site scripting. You would use it in any Node.js backend or browser-based form that needs to check user input. Install it with npm and call the functions directly. The tech stack is JavaScript, usable in Node.js or any browser.