Ghost/core/client/app/components/gh-form-group.js

import Ember from 'ember';

/**
 * Handles the CSS necessary to show a specific property state. When passed a
 * DS.Errors object and a property name, if the DS.Errors object has errors for
 * the specified property, it will change the CSS to reflect the error state
 * @param  {DS.Errors} errors   The DS.Errors object
 * @param  {string} property    Name of the property
 */
export default Ember.Component.extend({
    classNames: 'form-group',
    classNameBindings: ['errorClass'],

    errors: null,
    property: '',
    hasValidated: Ember.A(),

    errorClass: Ember.computed('errors.[]', 'property', 'hasValidated.[]', function () {
        var property = this.get('property'),
            errors = this.get('errors'),
            hasValidated = this.get('hasValidated');

        // If we haven't yet validated this field, there is no validation class needed
        if (!hasValidated || !hasValidated.contains(property)) {
            return '';
        }

        if (errors) {
            return errors.get(property) ? 'error' : 'success';
        }
    })
});