why we load jquery script in another server, why not own?

Question

Most sites load jquery just add link http://code.jquery.com. why we don't keep it our server . IS it waste loading time? what is the benefit?

Answer 1

The theory that jQuery would load quicker since it's cached from another website. Also there are rules on how many HTTP requests can hit a single domain name.

You can have the best of both worlds by using something mentioned on Best way to use Google's hosted jQuery, but fall back to my hosted library on Google fail

Answer 2

Try to google a little bit. The first link says:

1. Different domains Browsers limit the number of concurrent connections (file downloads) to a single domain. Most permit four active connections so the fifth download is blocked until one of the previous files has been fully retrieved. You can often see this limit in action when downloading many large files from the same site.

   CDN files are hosted on a different domain. In effect, a single CDN permits the browser to download a further four files at the same time.

2. Files may be pre-cached jQuery is ubiquitous on the web. There’s a high probability that someone visiting your pages has already visited a site using the Google CDN. Therefore, the file has already been cached by your browser and won’t need to be downloaded again.

3. High-capacity infrastructures You may have great hosting but I bet it doesn’t have the capacity or scalability offered by Google, Microsoft or Yahoo. The better CDNs offer higher availability, lower network latency and lower packet loss.

4. Distributed data centers If your main web server is based in Dallas, users from Europe or Asia must make a number of trans-continental electronic hops when they access your files. Many CDNs provide localized data centers which are closer to the user and result in faster downloads.

5. Built-in version control It’s usually possible to link to a specific version of a CSS file or JavaScript library. You can often request the “latest” version if required.

6. Usage analytics Many commercial CDNs provide file usage reports since they generally charge per byte. Those reports can supplement your own website analytics and, in some cases, may offer a better impression of video views and downloads.

7. Boosts performance and saves money A CDN can distribute the load, save bandwidth, boost performance and reduce your existing hosting costs — often for free.