Mascara HTML

$(document).ready(function(){

  $(".cpf").mask("999.999.999-99");
  $('.cpf').blur(function () {
    var id=$(this).attr("id");
    var val=$(this).val();
    var pattern = new RegExp(/[0-9]{3}[\.]?[0-9]{3}[\.]?[0-9]{3}[-]?[0-9]{2}/);

    if(val.match(pattern) == null){
      $("#"+id+"_error").html("Digite um CPF válido");
    }
    /* addition: for clearing if valid */
    else {
	  $("#"+id+"_error").html("");
    }
    /* end addition */
  });
});