<form class="login" id="login">
	<p class="title">Log in</p>
	<input type="text" placeholder="Username" id="username" autofocus/>
    <i class="fa material-icons md-14">account_box</i>
    <input type="password" placeholder="Password" id="password" />
    <i class="fa material-icons md-14">lock</i>
    <a href="#">Dimenticato la password?</a>
    <button onClick="btnLogin()">
		<i class="spinner"></i>
    	<span class="state">Log in</span>
	</button>
</form>


      function btnLogin() {
        alert("qui entra");

        var _username = document.getElementById("username").value;
        var _password = document.getElementById("password").value;

        alert(_username);
        alert(_password); /*questi si vedono*/

        $.get("../php/login.php", { username: _username , password: _password }, function(data) {
            console.log('post');
            if (data['loggedin'] == 1 && data['username'] != undefined)
              window.location.replace("../index.php");
        });
      }



<?php
	session_start();
	$mysqli = new mysqli("localhost", "root", "MySQLRootPassword@Mecq2018", "gdc2");

	$query = "SELECT idutente, username FROM utente WHERE username=? AND password=MD5(?);";

	if ($stmt = $mysqli->prepare($query)) {
		$stmt->bind_param("ss", $_GET["username"], $_GET["password"]);
		$stmt->execute();
		$stmt->bind_result($result["idutente"], $result["username"]);
		$stmt->fetch();
		$stmt->close();
	}

	echo json_encode($result);
?>