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              <html lang="ja">
<meta charset="UTF-8">
<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout-validation/2.0.3/knockout.validation.min.js"></script>
    <div data-bind="validationElement: email">
      <input type="text" placeholder="メールアドレスを入力してください" data-bind="textinput: email"/>
      <p class="text-danger" data-bind="validationMessage: email"></p>


              .has-error input {
  border: 1px solid red;
.text-danger {
  color: red;
              $(function() {
    function myViewModel() {
        var self = this;
        self.email = ko.observable().extend({
            required: {
                message: '必須項目です!'
            email: {
                message: 'メールアドレスの記述が間違っています!'

        insertMessages: false,
        errorElementClass: 'has-error'
    var viewModel = ko.validatedObservable(new myViewModel());
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