Validate input field on submit - knockout-validation

Question

Im tryinf to validate this input field when i click on Submit button. What happens is when I click on the submit button and the textbox is empty it alert thank you,however it should alert Please check your submission
Html
<div id="newTest">
<fieldset>
<div class="row">
<label>Last name:</label>
<input type="text" data-bind="value: lastName" />
</div>
</fieldset>
<fieldset>
<button type="button" data-bind='click: submit'>Submit</button>
</fieldset>
</div>
Javascript
<script src="~/Scripts/knockout-3.5.0.js"></script>
<script src="~/Scripts/knockout.validation.min.js"></script>
<script>
var viewModel = function () {
ko.validation.rules.pattern.message = 'Invalid.';
ko.validation.init({
registerExtenders: true,
messagesOnModified: true,
insertMessages: true,
parseInputAttributes: true,
messageTemplate: null
}, true);
var self = this;
self.lastName = ko.observable().extend({ required: true }),
self.submit = function () {
if (viewModel.errors().length === 0) {
alert('Thank you.');
}
else {
alert('Please check your submission.');
viewModel.errors.showAllMessages();
}
};
};
viewModel.errors = ko.validation.group(viewModel);
var viewModel2 = new viewModel();
ko.applyBindings(viewModel2, document.getElementById("newTest"));
</script>

Answer 1

Since you are initializing viewModel2 as new viewModel(), these two lines of code:
viewModel.errors = ko.validation.group(viewModel);
var viewModel2 = new viewModel();
should be:
var viewModel2 = new viewModel();
viewModel.errors = ko.validation.group(viewModel2);
It's also unclear to me why you wrote this the way you did. It could be simpler IMO. Here's an example (JSFiddle: https://jsfiddle.net/vwuazfg0/):
ko.validation.rules.pattern.message = 'Invalid.';
ko.validation.init({
registerExtenders: true,
messagesOnModified: true,
insertMessages: true,
parseInputAttributes: true,
messageTemplate: null
}, true);
var viewModel = {
lastName : ko.observable().extend({ required: true }),
submit : function () {
if (viewModel.errors().length === 0) {
alert('Thank you.');
}
else {
alert('Please check your submission.');
viewModel.errors.showAllMessages();
}
}
};
viewModel.errors = ko.validation.group(viewModel);
ko.applyBindings(viewModel, document.getElementById("newTest"));