Knockout Validation - Dont validate input when empty + evaluate when submit

Question

check this fiddle:

http://jsfiddle.net/bhzrw01s/

I was trying to do 2 things:

First: Dont validate when the field is empty. I know there is a onlyif option.. but is there something easier?

Second: I need something to run the validation when i click on submit (If you test my fiddle, the error messages will pop, but wont apply the errorClass css)

Thanks :D

css:

input.error {
    color: red;
    border-color: red;    
}

js:

ko.validation.configure({
    insertMessages: false,
    decorateElement: true,
    errorElementClass: 'error',
    messagesOnModified: false    
});

function SignInViewModel() {

    var self = this;
    self.userName = ko.observable().extend({
        required: true
    });
    self.password = ko.observable().extend({
        required: true
    });

    self.errors = ko.validation.group(self);
    self.login = function (e) {

        if (self.errors().length == 0) {
            alert('No errors');
        } else {
            this.errors().forEach(function(data) {
               alert(data);
        });
            //self.errors.showAllMessages(true);
        }
    }

}
$(function () {
    ko.applyBindings(new SignInViewModel());
});

html :

<form>
<fieldset>
    <legend>User: <span data-bind='text: errors().length'></span> errors</legend>
    <label>User name: <input data-bind='value: userName' type="text"/></label><br/>
    <label>Password: <input data-bind='value: password' type="password"/></label>

</fieldset>
<button type="button" data-bind='click: login'>Login</button>
</form>

Answer 1

The first solution will do 90% of what you are asking. It will not display any validation until the user hits submit, or until they delete a previously populated field. Once they break the seal (so to speak), they will receive real time validation feedback for that field. This is the solution I would use because it is how knockout validation was intended to behave.

http://jsfiddle.net/k08m4dfx/

    self.login = function (e) {
        if (self.errors().length > 0) {
            self.errors.showAllMessages(true);
            this.errors().forEach(function(data) {
               alert(data);
            });
        }
    }

If for some reason you have to defer all validation feedback until they click, then you could mess with the isModified flag to get the behavior you want. It seems a little kludgy to me though.

http://jsfiddle.net/zd97gjg4/

    ko.extenders.deferValidation = function (target, option) {
        if (option) {
            target.subscribe(function(){
                target.isModified(false);
            });
        }

        return target;
    };

    self.userName = ko.observable().extend({
        required: {message: 'User name is required' },
        deferValidation: true
    });

    self.password = ko.observable().extend({
        required: {message: "Password is required" },
        deferValidation: true
    });