Best way to link to jQuery files [duplicate]

Question

Is it better, in terms of site performance/speed, to link out to jquery, like this:

<script src="http://code.jquery.com/jquery-1.9.1.js"></script>

or to put the files on the server and link to them from there instead, like this:

<script src="js/jquery-1.9.1.js"></script>

Answer 1

It depends who has the faster server, right? :)

There are a few advantages with code.jquery.com:

1. It's very common. Users are likely to already have that file cached if they've been to another site that uses that file.

2. It's probably geographically load balanced. It could load faster for users who are far away from your web server.

Answer 2

As someone else mentioned, a local fallback is always a good idea, but you should also set the IE vs non-IE versions appropriately. Something simple like this should do the trick:

<!--[if lt IE 9]>
    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js""></script>
<![endif]-->
<!--[if gte IE 9]><!-->
    <script src="//ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
<!--<![endif]-->

<script>
    if (!window.jQuery) {
        document.write('<script src="/path/to/your/jquery"><\/script>');
    }
</script>

The first part is the conditional if for jQuery built with workarounds for older IE vs the faster, more efficient jQuery 2.0 version. This uses the Google CDN since that has both http and https versions, whereas code.jquery.com only has http. If https is not a concern, though, the code.jquery.com CDN is usually faster.

The second piece is checking if window.jQuery was created, and if not, use the local version.

The benefit to using a CDN version vs local version is just speed. Not only is their server bandwidth likely much (MUCH) larger than yours, most browsers have accessed that version before and have it stored in cache so the browser doesn't need to redownload it.

Answer 3

The best way to attach jQuery (or any library that google cdn is sharing) is:

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="js/vendor/jquery-1.9.1.min.js"><\/script>')</script>

This code links jQuery from CDN (this way is better because user could ALREADY HAVE this jQuery ver. in browser cache). After that code checks is jQuery successfully loaded (maybe CDN was down or something...) and if it's not it attaches the local version of jQuery lib to your page.

This code is used in html5 boilerplate.