What is the danger in including the same JavaScript library twice?

Question

One of the webapps I\'m working in is made up of many partial HTML files. If the partial requires a JavaScript library such as YUI, the YUI library is included in the partia

Answer 1

The browser will cache the file, downloading it only once. It will be executed more than once however. So the performance impact is negligible, but the correctness impact might not be.