title: Cannot call method 'toString' of undefined | There is something wrong with my code?
body: <p>Apparently my script is right, could someone help me with this? When I see the console it shows the message <code>Cannot call method 'toString' of undefined</code>.</p>
  
  <p>Could it be a problem with the ID selector? Can I use just one function instead of using one  for validation and another to run my function?</p>
  
  <pre><code>/* ==== CPF Validator ==== */
  function validar_cpf(cpf)
  {
      regex = /\./g;
      cpf = cpf.toString().replace(regex,'');
      cpf_split = cpf.split('-');
      numero = cpf_split[0];
      dv = cpf_split[1];
      numero_init = numero.toString() + dv.toString();
  
      if(numero_init.length &lt; 11)
          return false
  
      var somatorio = 0;
      for(i = 10, n = 0; i &gt;= 2 ; i--, n++){
          m = numero.charAt(n) * i;
          somatorio += m;
      }
  
  
      dv1 = somatorio / 11;   
      dv1 = parseInt(dv1);
  
      resto = somatorio % 11;
  
      if(resto &lt; 2)
          dv1 = 0;
      else
          dv1 = Math.abs(11 - resto);
  
      numero += dv1.toString();
  
      somatorio = 0;
      for(i = 11, n= 0; i &gt;= 2 ; i--, n++ ){
          m = numero.charAt(n) * i;
          somatorio += m;
      }
  
      resto = somatorio % 11;
  
      if(resto &lt; 2)
          dv2 = 0;
      else
          dv2 = 11 - resto;
  
      numero += dv2.toString();
  
      if(numero == numero_init)
          return true;
      else
          return false;
  }
  
  function ValidaCpf()
  {
      if (validar_cpf(cpf))
      {
          document.getElementById('first-cpf').classList.add('hide');
          document.getElementById('second-cpf').classList.remove('hide');     
          document.getElementById('cpf').classList.add('form_invalido');              
          document.getElementById('cpf').classList.remove('form_valido');             
      }
      else {
          document.getElementById('first-cpf').classList.remove('hide');
          document.getElementById('second-cpf').classList.add('hide');        
          document.getElementById('cpf').classList.remove('form_invalido');               
          document.getElementById('cpf').classList.add('form_valido');                                    
      }       
  }
  </code></pre>