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HTML

              
                <!-- code from bootstrap documentation -->
<form class="needs-validation" id="validation-test">
    <div class="form-row">
        <div class="col-md-4 mb-3">
            <label for="validationCustom01">First name</label>
            <input type="text" class="form-control" id="validationCustom01" placeholder="First name" value="" required data-pattern="text">
            <div class="valid-feedback">
                Looks good!
            </div>
            <div class="invalid-feedback">
                please enter a valid name
            </div>
        </div>
        <div class="col-md-4 mb-3">
            <label for="validationCustom02">Numbers</label>
            <input type="text" class="form-control" id="validationCustom02" placeholder="numbers" value="" required data-pattern="numbers">
            <div class="valid-feedback">
                Looks good!
            </div>
            <div class="invalid-feedback">
                please enter a valid number
            </div>
        </div>
        <div class="col-md-4 mb-3">
            <label for="validationCustomUsername">Email</label>
            <div class="input-group">
                <div class="input-group-prepend">
                    <span class="input-group-text" id="inputGroupPrepend">@</span>
                </div>
                <input type="text" class="form-control" id="validationCustomUsername" placeholder="Email" aria-describedby="inputGroupPrepend" required data-pattern="email">
                <div class="invalid-feedback">
                    please enter a valid email address
                </div>
                <div class="valid-feedback">
                    Looks good!
                </div>
            </div>
        </div>
    </div>
    <div class="form-group">
        <div class="form-check">
            <input class="form-check-input" type="checkbox" value="" id="invalidCheck" required>
            <label class="form-check-label" for="invalidCheck">
                Agree to terms and conditions
            </label>
            <div class="invalid-feedback">
                You must agree before submitting.
            </div>
        </div>
    </div>
    <button class="btn btn-primary" type="submit">Submit form</button>
</form>
              
            
!

CSS

              
                form {
    padding: 20px;
}
              
            
!

JS

              
                 class FormValidator {
     constructor(config) {
      /**
       * @description creates new validation model and provides validation patterns
       * @type {FormValidatorModel} config
       */
      this.config = new FormValidatorModel(config);

      /**
       * @description form elements
       * @type {HTMLElement} form
       */
      this.form = document.querySelector(this.config.selector);

      /**
       * @description form element
       * @type {NodeList} inputs
       */
      this.inputs = this.form.querySelectorAll(this.config.inputTypes);
         
       /**
       * @description init validation script
       */
      this._init();
     }
     
     _init() {
         // disable HTML5 Browser form validation
         this.form.setAttribute('novalidate', true);

         this.form.addEventListener('submit', e => {
             e.preventDefault();
             this.handleSubmit();
         });
         
         this._addValidationPatterns()
     }
     
     /**
    * @description handle form validtion
    */
     handleSubmit() {
        if (this.form.checkValidity()) {
            // submit the form if validation is successful
            this.submit();
        } else {
            this.validateForm();
        }
     }
     
    /**
    * @description validate current form
    */
     validateForm() {
         this.form.classList.add('was-validated');
         
         this.inputs.forEach(el => {
             if (!el.validity.valid) {
                 // handle custom error ....
             }
         });
     }
     
     /**
    * @description set the validation pattern for each input of the form
    * @private
    */
   _addValidationPatterns() {
      let pattern;

      // add validation patterns from config model
      this.inputs.forEach(el => {
         if (el.type != 'hidden') {
            pattern = this.config.validatorPatterns[el.dataset.pattern || el.type || 'text'];

            if (pattern) {
               el.setAttribute('pattern', pattern);
            }
         }
      });
   }
     
   submit() {
       // submit the form :)
       this.form.classList.remove('was-validated');
   }
 }
     
 class FormValidatorModel {
     constructor(config = {}) {
     /**
       * @description possible input types for validation
       * @type {*|string} inputTypes
       */
      this.inputTypes = config.inputTypes || 'select, textarea, input';
     
      /**
       * @description form selector for validation
       * @type {*|string} selector
       */
      this.selector = config.selector || '';
         
       /**
       * @description email validator pattern
       * @type {string} email
       */
      this.email = '^([a-zA-Z0-9_\\-\\.]+)@([a-zA-Z0-9_\\-\\.]+)\\.([a-zA-Z]{2,5})$';
         
       /**
       * @description not only number validator pattern
       * @type {string}
       */
      this.notOnlyNumbers = '^[0-9]*$';

      /**
       * @description only numbers validator pattern
       * @type {string}
       */
      this.onlyNumbers = '[0-9]*';
         
       /**
       * @description handles all current active validator patterns
       * @type {Object} validatorPatterns
       */
         
       /**
       * @description text validator pattern
       * @type {string} text
       */
      this.text = '';
         
      this.validatorPatterns = {
         text: this.text,
         email: this.email,
         notOnlyNumbers: this.notOnlyNumbers,
         numbers: this.onlyNumbers
      };
     }
 }

const validator = new FormValidator({
    selector: '#validation-test'
});
              
            
!
999px

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