Feedback.js

var Feedback = Backbone.Model.extend({

    url: '/feedback',

    defaults: {
        'email': '',
        'website': '',
        'feedback': ''
    },

    validate: function (attrs) {
        var errors = [];

        if (!attrs.email) {
            errors.push({name: 'email', message: 'Please fill email field.'});
        }
        if (!attrs.feedback) {
            errors.push({name: 'feedback', message: 'Please fill feedback field.'});
        }

        return errors.length > 0 ? errors : false;
    }

});

FeedbackApp.js

$(function () {
    var model = new Feedback();
    var view = new FeedbackFormView ({model: model});
    
    $('#app').html(view.render().el);
});

FeedbackFormView.js

var FeedbackFormView = Backbone.View.extend({
   className: 'row',

    template: '\
        <form>\
            <legend>Share the feedback</legend>\
            <div class="control-group email">\
                <label>Email</label>\
                <input type="text" id="email" placeholder="Your email address...">\
                <span class="help-inline"></span>\
            </div>\
            <div class="control-group website">\
                <label>Web site</label>\
                <input type="text" id="website" placeholder="Your website...">\
                <span class="help-inline"></span>\
            </div>\
            <div class="control-group feedback">\
                <label>Feedback</label>\
                <textarea id="feedback" class="input-xxlarge" placeholder="Feedback text..." rows="6"></textarea>\
                <span class="help-inline"></span>\
            </div>\
            <button type="submit" id="submit" class="btn">Submit</button>\
        </form>\
    ',

    events: {
        'click #submit': 'submitClicked'
    },

    render: function () {
        this.$el.html(this.template);

        return this;
    },

    submitClicked: function (e) {
        e.preventDefault();

        var me = this;
        var options = {
            success: function () {
                me.hideErrors();
            },
            error: function (model, errors) {
                me.showErrors(errors);
            }
        };

        var feedback = {
            email: this.$('#email').val(),
            website:  this.$('#website').val(),
            feedback: this.$('#feedback').val()
        };

        this.model.save(feedback, options);
    },

    showErrors: function(errors) {
        _.each(errors, function (error) {
            var controlGroup = this.$('.' + error.name);
            controlGroup.addClass('error');
            controlGroup.find('.help-inline').text(error.message);
        }, this);
    },

    hideErrors: function () {
        this.$('.control-group').removeClass('error');
        this.$('.help-inline').text('');
    }
});