text: class Textbox {     
      constructor(selector, regex) {
          this._value = '';
          this._elements = Array.from(document.querySelectorAll(selector));
          this._invalidSymbols = regex;
      }    
  
      get value() {
          return this._value;
      }    
  
      set value(v) {
          this._value = v;
  
          for (let i = 0; i < this._elements.length; i++) {
              this._elements[i].value = v;            
          }
  
          // judge score: 40 / 100
          // Unexpected error: Textbox value did not change.
          // TODO: 100 / 100
      }    
  
      get elements() {
          return this._elements;
      }
  
      isValid() {
          return !this._invalidSymbols.test(this.value);
      } 
  }
  
  // let textbox = new Textbox(".textbox", /[^a-zA-Z0-9]/);
  // let inputs = $('.textbox');
  
  // inputs.on('input', function () { console.log(textbox.value); });
  