如果按下F5，Google reCAPTCHA

I want to enable a Google reCAPTCHA if F5 is pressed. I have this code at the moment:

<html>
<head>
<title>HELLO</title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src='https://www.google.com/recaptcha/api.js'></script>
<script type="text/javascript">
document.onkeydown = fkey;
document.onkeypress = fkey
document.onkeyup = fkey;

var wasPressed = false;

function fkey(e){
        e = e || window.event;
       if( wasPressed ) return; 

        if (e.keyCode == 116) {
             alert("f5 pressed");
          // here the Google reCAPTCHA code have to come.
            wasPressed = true;
        }else {
            alert("Window closed");
        }
 }
</script>
</head>
<body>
<p>If you press F5 you will get a Google reCAPTCHA</p>
</body>
</html>

<div class="g-recaptcha" data-sitekey="6LehRSETAAAAAIl2C3nRFguErdFn02smPN_vtPro"></div>

This is the code to show up the Google reCAPTCHA.

I hope someone can help me, so I can go further. Thanks :D

</div>

<html>
<head>
<title>HELLO</title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src='https://www.google.com/recaptcha/api.js'></script>
<script type="text/javascript">
document.onkeydown = fkey;
document.onkeypress = fkey
document.onkeyup = fkey;

var wasPressed = false;

function fkey(e){
        e = e || window.event;
       if( wasPressed ) return; 

        if (e.keyCode == 116) {
            // here the Google reCAPTCHA code have to come.
            $('.g-recaptcha').show();
            e.preventDefault();
            wasPressed = true;
        }else {
            alert("Window closed");
        }
 }
</script>
</head>
<body>
<p>If you press F5 you will get a Google reCAPTCHA</p>
 <div class="g-recaptcha" data-sitekey="6LehRSETAAAAAIl2C3nRFguErdFn02smPN_vtPro" style="display:none;"></div>
</body>
</html>

</div>