how to open javascript code after website load?

my website loading time is too much for zendesk chat, when i remove zendesk chat the website loading time under 2 seconds here is my zendesk code...

<script>
window.$zopim||(function(d,s){var z=$zopim=function(c){z._.push(c)},$=z.s= d.createElement(s),e=d.getElementsByTagName(s)[0];z.set=function(o){z.set._.push(o)};z._=[];z.set._=[];$.async=!0;$.setAttribute("charset","utf-8");$.src="//v2.zopim.com/?14mOH4BM2323DFADFSAS";z.t=+new Date;$.type="text/javascript";e.parentNode.insertBefore($,e)})(document,"script");
</script>