Two main factors increase the odds of a script being duplicated in a single web page: team size and number of scripts.

It takes a significant amount of resources to develop a web site, especially if it’s a top destination.In addition to the core team building the site, other teams contribute to the HTML in the page for things such as advertising, branding (logos, headers, footers,etc.), and data feeds (news stories, sports scores, TV listings, etc.). With so many people from different teams adding HTML to the page, it’s easy to imagine how the same script could be added twice.For example, two developers might be contributing JavaScript code that requires manipulating cookies, so each of them includes the
company’s cookies.js script.Both developers are unaware that the other has already added the script to the page