viewmodel.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>
</head>
<body>
    <body>
        <div>
            <input type="text" id="content">
            <p id="show-content"></p>
        </div>
        <script>
            var obj = {}
            Object.defineProperty(obj, 'content', {
                get: function() {
                    return obj;
                },
                set: function(newValue) {
                    document.getElementById('content').value = newValue;
                    document.getElementById('show-content').innerHTML = newValue;
                }
            })
            document.addEventListener('keyup', function(e){
                obj.content = e.target.value;
            })
        </script>
    </body>
</body>
</html>