ConfirmedEmailValidator.js

// Requires Prototype.js
ConfirmedEmailValidator = Class.create(
{
    initialize: function(email_input, confirmation_input) {
        this.valid_class = 'valid'
        this.invalid_class = 'invalid'
        this.email_id = email_input
        this.confirmation_id = confirmation_input
        this.re = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/
        this.add_observers()
    },
    add_observers: function() {
        document.observe("dom:loaded", function() {
            this.email = $(this.email_id)
            this.confirmation = $(this.confirmation_id)
            this.email.observe('change', this.display_validity.bind(this))
            this.confirmation.observe('keyup', this.display_validity.bind(this))
        }.bindAsEventListener(this))
    },
    valid_email: function(){
        return (this.email.value.match(this.re) != null)
    },
    valid_confirmation: function() {
        return (this.confirmation.value.match(this.re) != null)
    },
    matching: function() {
        return (this.email.value == this.confirmation.value)
    },
    valid: function() {
        return (this.matching() && this.valid_email() && this.valid_confirmation() )
    },
    display_validity: function(){
        if (this.valid()) {
            this.email.removeClassName(this.invalid_class)
            this.email.addClassName(this.valid_class)
            this.confirmation.removeClassName(this.invalid_class)
            this.confirmation.addClassName(this.valid_class)
        } else {
            if (this.valid_email()) {
                this.email.removeClassName(this.invalid_class)
                this.email.addClassName(this.valid_class)
            } else {
                this.email.removeClassName(this.valid_class)
                this.email.addClassName(this.invalid_class)
            }
            if (this.valid_confirmation){
                this.confirmation.removeClassName(this.invalid_class)
                this.confirmation.addClassName(this.valid_class)
            } else {
                this.confirmation.removeClassName(this.valid_class)
                this.confirmation.addClassName(this.invalid_class)
            }
            if (!this.matching() ) {
                this.confirmation.removeClassName(this.valid_class)
                this.confirmation.addClassName(this.invalid_class)
            }
        }
    }
}
)