text: function calcular(){
      var num = document.getElementById('num');
      var tab = document.getElementById('tab');
      
      if(num.value.length == 0){
          alert('INPUT VAZIO')
      }
      else{
          tab.innerHTML = ``;
          num = Number(num.value);
          for(c = 1 ; c<=10 ; c++ ){
              var item = document.createElement('option');
              item.text =`${num} X ${c} = ${num*c}`;
              tab.appendChild(item);
          }
      }
  }