Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<head>
<link id="myLink" href="http://www.w3schools.com/jsref/domoarigato.htm" hreflang="ja">
</head>
<body>

<p>Click the button to change the language code of the linked document.</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
    document.getElementById("myLink").hreflang = "en-us";
    document.getElementById("demo").innerHTML = "The language code was changed from 'ja' to 'en-us'.";
}
</script>

</body>
</html>