When do you choose to load your javascript at the bottom of the page instead of the top?

Question

I have seen JavaScript libraries being loaded at the top and bottom of the page.

I would love to know when to make these choices. All the JavaScript code I\'ve writt

Answer 1

Yahoo says to Put Scripts at the Bottom. Google says something similar but not as clearly.

Answer 2

The reason you do it at the bottom of the page is because if you put it at the top of your page then the rendering of your page will wait for these files before it renders. This is why a lot of people put JavaScript at the bottom of the page as it allows the entire page to be rendered then the JavaScript is loaded.

There's very rarely any reason you'd want to put the JavaScript at the top of the page, and unless you have an explicit reason you want the JavaScript loaded in before the main page then put it at the bottom. Most optimization guides suggest putting it at the bottom for this reason.

Answer 3

Top: When having JavaScript events function on elements immediately is more important (so if you use a DOM Ready event to load everything, this is the wrong place)

Bottom: When loading the content is more important