text: function tabuada(){
  
      let num = document.getElementById('txtn')
      let tab = document.getElementById('seltab')
  
      if(num.value.length == 0){
          alert('Digite algum número!')
      }else{
          let n = Number(num.value)
          tab.innerHTML = ''
  
          for (let c = 0; c <= 10; c++) {
              let item = document.createElement('option')
              item.text = `${n} x ${c} = ${n*c}`
              tab.appendChild(item)
          }
      }
  }