Knockout Validation

HTML

<script src="https://raw.github.com/ericmbarnard/Knockout-Validation/master/Src/knockout.validation.js"></script>
<input data-bind="value: AuthorName"/> <br/>
<input data-bind="value: Name"/><br/>

Has errors: <span data-bind="text: errors().length != 0"></span>

JavaScript

ko.validation.configure({
    registerExtenders: true,
    messagesOnModified: true,
    insertMessages: true,
    parseInputAttributes: true,
    messageTemplate: null
});

function BookViewModel(bookObject) {
    var self = this;

    self.AuthorName = ko.observable(bookObject.AuthorName).extend({
        required: {
            message: "Please enter menu name"
        },
        minLength: 4,
        maxLength: 10
    });
    self.Name = ko.observable(bookObject.Name).extend({
        required: {
            message: "Please enter course name"
        },
        minLength: 4,
        maxLength: 10
    });
}

var data = {
    AuthorName: "Tom",
    Name: "Rider"
};
var viewModel = new BookViewModel(data);
viewModel.errors = ko.validation.group(viewModel);

ko.applyBindings(viewModel);