Bootstrap Forms Validation

Form validation is an essential part of web development to ensure that user input meets specified criteria before submission. Bootstrap provides built-in styles and JavaScript plugins for form validation, making it easy to implement validation rules and provide feedback to users. Here's how to use Bootstrap's form validation:

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1. Basic Form Structure

Start with a basic HTML form structure and include Bootstrap classes for styling:

<form class="needs-validation" novalidate>
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" required>
    <div class="invalid-feedback">Please enter a valid email address.</div>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

The needs-validation class on the form element indicates that Bootstrap should handle form validation. Each form control should have the required attribute to trigger validation.

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2. Feedback Messages

Provide feedback messages for validation errors using the invalid-feedback class:

<div class="form-group">
  <label for="exampleInputPassword1">Password</label>
  <input type="password" class="form-control" id="exampleInputPassword1" required>
  <div class="invalid-feedback">Please enter a password.</div>
</div>

The invalid-feedback element will be displayed when the input fails validation.

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3. Custom Feedback

You can also provide custom feedback messages using JavaScript and CSS. Add the is-invalid class to the form control to trigger the custom feedback:

<input type="text" class="form-control is-invalid" id="validationCustom01" required>
<div class="invalid-feedback">Please enter a valid username.</div>

Use JavaScript to toggle the is-invalid class based on validation results.

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4. JavaScript Initialization

Initialize Bootstrap's form validation JavaScript plugin by selecting the form element and calling the .validate() method:

document.addEventListener('DOMContentLoaded', function () {
  var forms = document.querySelectorAll('.needs-validation');
  Array.prototype.slice.call(forms).forEach(function (form) {
    form.addEventListener('submit', function (event) {
      if (!form.checkValidity()) {
        event.preventDefault();
        event.stopPropagation();
      }
      form.classList.add('was-validated');
    }, false);
  });
}, false);

This JavaScript snippet ensures that form validation is triggered on form submission.

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5. Additional Features

Bootstrap offers additional features for form validation, such as customizing validation states, handling validation with tooltips, and more. Refer to the Bootstrap documentation for advanced usage.

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Conclusion

Bootstrap's form validation functionality makes it easy to create robust and user-friendly forms with client-side validation. By following these guidelines and examples, you can enhance the validation experience for users and improve the overall usability of your web forms.