how to calculate page rendering time with or without any javascript or with multiple javascript separately

how to calculate page rendering time with or without any javascript or with multiple JavaScript separately?

I want to know how much page will go slow if i use any javascript/jquery with plugin/ multipl开发者_运维技巧e javascript/jquery plugin files etc.?

javascript code in any form inline, in-page code, external file.

---

A good option is to use Firebug (its "Net" panel) combined with PageSpeed (a Firebug plugin provided by Google) for testing your different configurations.

Update: Forgot to mention YSlow.