未捕获的TypeError：无法读取未定义的属性'trackPid'

<script src="//platform.twitter.com/oct.js" type="text/javascript"></script>

<script type="text/javascript">
if(typeof twttr!=='undefined' && twttr && typeof twttr.conversion==='function' && typeof twttr.conversion.trackPid==='function'){
   twttr.conversion.trackPid('xxxx',{tw_sale_amount:0,tw_order_quantity:0});
        }
            </script>
<script src="//platform.twitter.com/oct.js" typ