How do I Add this Script in my game ?

I have Java Script like below:

<script language="javascript" type="text/javascript">

var _sa = _sa || [];

_sa.push(["initialize","","","","",""]);

_sa.push(['displayAd']);

(function () {

var sa = document.createElement('script');

sa.type = 'text/javascript';

sa.async = true;

sa.src = '//ads.appnext.com/ad/source.js';

var s = document.getElementsByTagName('script')[0];

s.parentNode.insertBefore(sa, s);

})();

</script>

when I am using this plugin https://www.scirra.com/forum/viewtopic.php?t=64104&start=0

to call this script, its giving me syntax error .

I do not have much idea about Java Script .

Why its giving me syntax error ?