问如何使用jquery $.post()方法提交表单值

EN

<meta charset="UTF-8">
<title>Form Page</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="process.php" method="post" id="reg-form">
        Username: <input type="text" id="username" name="username">
        <br>
        Password: <input type="password" id="password" name="password">
        <br>
        <button type="submit" id="submit-btn">Traditional Submit</button>
        <button type="button" id="post-btn">$.Post Submit</button>
</form>
<script>
    $("#post-btn").click(function(){        
        $.post("process.php",function(data){
            alert(data);
        });
    });
</script>

<?php
$username=$_POST["username"];
$password=$_POST["password"];
echo "Username: ".$username;
echo "<br>";
echo "Password: ".$password;?>