Code don't load amazon ad dynamically

The code don't load that script dynamically. The ad from Amazon is not created in this way.

<script>
 //create script tag
var headID = document.getElementById("id1");         
var newScript = document.createElement('script');
newScript.type = 'text/javascript';

//add amazon code
newScript.text=" amzn_assoc_ad_type = 'contextual';amzn_assoc_tracking_id = 'myid';.....";
//append script
headID.appendChild(newScript);

//create script tag to load amazon

var headID = document.getElementById("id1");         
var newScript = document.createElement('script');
newScript.type = 'text/javascript';
newScript.src = 'http://ift.tt/1yXAPNX';
headID.appendChild(newScript);
</script>