xmlhttp=new XMLHttpRequest();

<form id="formulario" action=""  method="POST">
        <div class="form-group">
          <label for="idnombre">Nombre:</label>
          <input type="text" class="form-control" id="idnombre" name="namenombre" placeholder="Ingresar Nombre">
        </div>

        <div class="form-group">
          <label for="idapellido">Apellido:</label>
          <input type="text" class="form-control" id="idapellido" name="nameapellido" placeholder="Ingresar Apellido">
        </div>

        <div class="form-group">
          <label for="idedad">Edad:</label>
          <input type="text" class="form-control" id="idedad" name="nameedad" placeholder="Ingresar Edad">
        </div>

        <button type="submit" id="button" class="btn btn-default">Registrar</button>
</form>

<?php
$servername = "localhost";
$username = "username";
$password = "";
$dbname = "demo";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

        $nombre = $_POST['namenombre'];
        $apellido = $_POST['nameapellido'];
        $edad = $_POST['nameedad'];


$sql = "INSERT INTO persona (nombre, apellido, edad) VALUES ('$nombre', '$apellido', '$edad')";

if ($conn->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();

?>

<div class="alert alert-success">
    <a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>
    <strong>Success!</strong> This alert box could indicate a successful or positive action.
  </div>