change iframe src by javascript

                                    <script type="text/javascript">
function iframeDidLoad() {
    alert('Done');
}

function newSite() {
    var sites = ['http://getprismatic.com',
                 'http://gizmodo.com/',
                 'http://lifehacker.com/']

    document.getElementById('myIframe').src = sites[Math.floor(Math.random() * sites.length)];
}    
</script>
<input type="button" value="Change site" onClick="newSite()" />
<iframe id="myIframe" src="http://getprismatic.com/" onLoad="iframeDidLoad();"></iframe>

                                    //change iframe src get the iframe then . and src and provide a value
 document.getElementById("myFrame").src = "https://facobook.com"; 

                                    Do not use Inquisitive Iguana's answer! Notice the spelling of facebook in https://facobook.com. Visiting the webpage downloads malware onto your system

Message from my antivirus on my mac: "We've blocked the threat URL:Mal on http://dt.gnpe.com/ptmd from being downloaded."