[javascript] What is jQuery Unobtrusive Validation?

I know what the jQuery Validation plugin is. I know the jQuery Unobtrusive Validation library was made by Microsoft and is included in the ASP.NET MVC framework. But I cannot find a single online source that explains what it is. What is the difference between the standard jQuery Validation library and the "unobtrusive" version?

With the unobtrusive way:

• You don't have to call the validate() method.
• You specify requirements using data attributes (data-val, data-val-required, etc.)

Jquery Validate Example:

<input type="text" name="email" class="required">
<script>
        $(function () {
            $("form").validate();
        });
</script>

Jquery Validate Unobtrusive Example:

<input type="text" name="email" data-val="true" 
data-val-required="This field is required.">  

<div class="validation-summary-valid" data-valmsg-summary="true">
    <ul><li style="display:none"></li></ul>
</div>

For clarification, here is a more detailed example demonstrating Form Validation using jQuery Validation Unobtrusive.

Both use the following JavaScript with jQuery:

  $("#commentForm").validate({
    submitHandler: function(form) {
      // some other code
      // maybe disabling submit button
      // then:
      alert("This is a valid form!");
//      form.submit();
    }
  });

The main differences between the two plugins are the attributes used for each approach.

jQuery Validation

Simply use the following attributes:

• Set required if required
• Set type for proper formatting (email, etc.)
• Set other attributes such as size (min length, etc.)

Here's the form...

<form id="commentForm">
  <label for="form-name">Name (required, at least 2 characters)</label>
  <input id="form-name" type="text" name="form-name" class="form-control" minlength="2" required>
  <input type="submit" value="Submit">
</form>

jQuery Validation Unobtrusive

The following data attributes are needed:

• data-msg-required="This is required."
• data-rule-required="true/false"

Here's the form...

<form id="commentForm">
  <label for="form-x-name">Name (required, at least 2 characters)</label>
  <input id="form-x-name" type="text" name="name" minlength="2" class="form-control" data-msg-required="Name is required." data-rule-required="true">
  <input type="submit" value="Submit">
</form>

Based on either of these examples, if the form fields that are required have been filled, and they meet the additional attribute criteria, then a message will pop up notifying that all form fields are validated. Otherwise, there will be text near the offending form fields that indicates the error.

References: - jQuery Validation: https://jqueryvalidation.org/documentation/

jQuery Validation Unobtrusive Native is a collection of ASP.Net MVC HTML helper extensions. These make use of jQuery Validation's native support for validation driven by HTML 5 data attributes. Microsoft shipped jquery.validate.unobtrusive.js back with MVC 3. It provided a way to apply data model validations to the client side using a combination of jQuery Validation and HTML 5 data attributes (that's the "unobtrusive" part).