validate.js

validate.js is a lightweight JavaScript form validation library inspired by CodeIgniter.

Features

• Validate form fields from over a dozen rules
• No dependencies
• Customizable Messages
• Supply your own validation callbacks for custom rules
• Chainable customization methods for ease of declaration
• Works in all major browsers, (even IE6!)
• Modeled off the CodeIgniter form validation API

How to use

var validator = new FormValidator('example_form', [{
    name: 'req',
    display: 'required',    
    rules: 'required'
}, {
    name: 'alphanumeric',
    rules: 'alpha_numeric'
}, {
    name: 'password',
    rules: 'required'
}, {
    name: 'password_confirm',
    display: 'password confirmation',
    rules: 'required|matches[password]'
}, {
    name: 'email',
    rules: 'valid_email'
}, {
    name: 'minlength',
    display: 'min length',
    rules: 'min_length[8]'
}], function(errors) {
    if (errors.length > 0) {
        // Show the errors
    }
});

Documentation

You can view everything at http://rickharrison.github.com/validate.js