Relevant JS snippet for add students validation.

add-students-validation.js

if (exports.addStudentsValidNames().length) {
            exports.addStudentsCheckingUsernames(true);
            $.post('/classroom/check', {
                students: JSON.stringify(exports.addStudentsValidNames())
            }, function (data) {
                var hasErrors;
                data.each(function (i) {
                    i.transfer = ko.observable(null);
                    i.errorFields = [];
                    i.warningFields = [];
                    if (i.errors instanceof Array) {
                        i.errors.each(function (j, index) {
                            var fields = j.match(fieldsRex);
                            if (fields.length && !index) {
                                i.errors[index] = j.remove(fields[0]);
                                i.errorFields = JSON.parse(fields[0]).fields;
                            }
                        });
                    }
                    if (i.warnings instanceof Array) {
                        i.warnings.each(function (j, index) {
                            var fields = j.match(fieldsRex);
                            if (fields.length && !index) {
                                i.warnings[index] = j.remove(fields[0]);
                                i.warningFields = JSON.parse(fields[0]).fields;
                            }
                        });
                    }
                    i.firstName = ko.observable(i.firstName);
                    i.lastName = ko.observable(i.lastName);
                    i.username = ko.observable(((exports.addStudentsMode() == 'needUsername') && (reValidate === true)) ? i.suggestion : i.username);
                    i.password = ko.observable(i.password);
                    i.firstNameEditable = ko.observable(false);
                    i.lastNameEditable = ko.observable(false);
                    i.usernameEditable = ko.observable(false);
                    i.passwordEditable = ko.observable(false);
                    i.mode = exports.addStudentsMode();
                    i.invalidate = function () {
                        exports.addStudentsHasPotentialErrors(true);
                    };
                    i.editing = function (editing) {
                        exports.addStudentsEditingFields(editing);
                    };
                    i.remove = function () {
                        var _data = exports.addStudentsNames();
                        _data.remove(i);
                        hasErrors = _data.any(function (j) {
                            return j.errors.length;
                        });
                        _data.each(function (j) {
                            j.hasErrors(hasErrors);
                        });
                        exports.addStudentsNames.valueHasMutated();
                    };
                });
                hasErrors = data.any(function (i) {
                    return i.errors.length;
                });
                data.each(function (i) {
                    i.hasErrors = ko.observable(hasErrors);
                });
                exports.addStudentsNames(data);
                exports.addStudentsCheckingUsernames(false);
            });
        }