在浏览器中的网页上多次执行相同的java脚本

What are the scenarios for a webpage to execute same java script multiple times? YSlow states duplicate java script execution should be avoided as it has performance implications but what about running same JS for creating multiple frames on a page. Is this a valid scenario? Please let me know if there are any valid scenarios where you need to have multiple duplicate JS execute in the browser?What are the scenarios for a webpage to execute