test3.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>

    <div>
        <p>Some words here</p>
        <button id="btn1">Add</button>
    </div>

    <div id="test-div">
        <input type="text" placeholder="already here">
    </div>

    <script>
        $(document).ready(function(){
            $("#btn1").click(function(){
                $("#test-div").append('<input type="text" placeholder="A New one">');
            });
        });
    </script>

    <script src="js/model.js"></script>
</body>
</html>