bootstrap error class input code example

Example 1: bootstrap 4 input error

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">

<!--
  Title: bootstrap 4 input error
-->
<!--Go to https://www.w3schools.com/bootstrap4/bootstrap_forms.asp for more info-->
<form action="/action_page.php" class="was-validated">
  <div class="form-group">
    <label for="uname">Username:</label>
    <input type="text" class="form-control" id="uname" placeholder="Enter username" name="uname" required>
    <div class="valid-feedback">Valid.</div>
    <div class="invalid-feedback">Please fill out this field.</div>
  </div>
  <div class="form-group">
    <label for="pwd">Password:</label>
    <input type="password" class="form-control" id="pwd" placeholder="Enter password" name="pswd" required>
    <div class="valid-feedback">Valid.</div>
    <div class="invalid-feedback">Please fill out this field.</div>
  </div>
  <div class="form-group form-check">
    <label class="form-check-label">
      <input class="form-check-input" type="checkbox" name="remember" required> I agree on blabla.
      <div class="valid-feedback">Valid.</div>
      <div class="invalid-feedback">Check this checkbox to continue.</div>
    </label>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

Example 2: bootstrap email address validation

<form> <!--make sure you add this inside a form-->
  <div class="form-group"> <!--required to start the form container-->
    <label for="InputEmail">Email address</label> <!--"for" needs to match the "id" on the next line to bind it-->
    <input type="email" class="form-control" id="InputEmail" placeholder="Enter email"> <!--id, class, and type are required for it too look right, placeholder will edit the text inside the input box-->
    <small class="form-text">We'll never share your info.</small> <!--applies small underlining text-->
  </div>
  <div class="form-group">
    <label for="Password">Password</label>
    <input type="password" class="form-control" id="Password" placeholder="Password">
  </div>
  <div class="form-check">
    <input type="checkbox" class="form-check-input" id="Check">
    <label class="form-check-label" for="Check">Check out</label>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>