HTML5 validation when the input type is not "submit"

I may be late, but the way I did it was to create a hidden submit input, and calling it's click handler upon submit. Something like (using jquery for simplicity):

<input type="text" id="example" name="example" value="" required>
<button type="button"  onclick="submitform()" id="save">Save</button>
<input id="submit_handle" type="submit" style="display: none">

<script>
function submitform() {
    $('#submit_handle').click();
}
</script>

You should use form tag enclosing your inputs. And input type submit.
This works.

<form id="testform">
<input type="text" id="example" name="example"  required>
<button type="submit"  onclick="submitform()" id="save">Save</button>
</form>

Since HTML5 Validation works only with submit button you have to keep it there. You can avoid the form submission though when valid by preventing the default action by writing event handler for form.

document.getElementById('testform').onsubmit= function(e){
     e.preventDefault();
}

This will give your validation when invalid and will not submit form when valid.

The HTML5 form validation process is limited to situations where the form is being submitted via a submit button. The Form submission algorithm explicitly says that validation is not performed when the form is submitted via the submit() method. Apparently, the idea is that if you submit a form via JavaScript, you are supposed to do validation.

However, you can request (static) form validation against the constraints defined by HTML5 attributes, using the checkValidity() method. If you would like to display the same error messages as the browser would do in HTML5 form validation, I’m afraid you would need to check all the constrained fields, since the validityMessage property is a property of fields (controls), not the form. In the case of a single constrained field, as in the case presented, this is trivial of course:

function submitform() {
  var f = document.getElementsByTagName('form')[0];
  if(f.checkValidity()) {
    f.submit();
  } else {
    alert(document.getElementById('example').validationMessage);
  }
}