如何在运行脚本之前检查一个元素是否已加载到页面上?

So I am creating my page in my companies template, which only allow us access to the body of the page. We don't have access to the head tag and there are scripts loaded on a lower part of the page that we don't have access to. One of these scripts dynamically loads an element onto the page. I need to run another script on that element, but because the element isn't loaded on the page until after my script has already ran I can't access that element. Is there a way I can check to see if that element has already been loaded on the page before running my script?So I am creating my page in my companies templa