Look at http://fh3jsvalidator.googlecode.com/svn/trunk/ for the latest version (0.5a)!! The downloadable zip file can be out of date.

I've created a new javascript validation script which validates form fields. The validator methods are ported from the PHP Formhandler project

The javascript syntax is pretty simple:

window.onload = function(){
	// Add the elements to the validator
	Var Validator = new jsValidator();
	Validator.elmts = {
		name: {
			validator: 'IsString',
			msg: 'This field must be a valid string'
		},
		age: {
			validator: 'IsDigit',
			msg: 'This field must be a digit'
		},
		description: {
			validator: '_IsText',
			msg: 'This textarea can be empty, or must be a valid text'
		}	
	}
	// Fire the validator
	Validator.init();
}

you can also create your own validate functions or your own regular expression

I've also created an extend class for formhandler to auto generate the validation code.