Tryit Editor v2.7

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<img src="pic_bulboff.gif" width="100" height="180">

<p>Click the button to change the src attribute's value of the image above.</p>

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

<script>
function myFunction() {
    var x = document.getElementsByTagName("IMG")[0];
    x.getAttributeNode("src").value = "pic_bulbon.gif";
}
</script>

</body>
</html>