Loading libraries from CDNs is generally perceived as a simple way to speed boost the loading time of your website, but don't stop your thinking from going further ! The cons outnumber the pros by a large amount if you ask me... lets mention a few :
- Your website will not work when a CDN is down if your code is depending on it ! (even if your website's itself is not down)
- A new TCP connection must be initiated for the CDN because it comes from an other domain (which can add more precious milliseconds to your loading time).
- It's a huge security risk ! You are willingly injecting external JavaScript code into your website, imagine if someone hacks that CDN and inject malicious code directly into your website... You won't even notice !
- It's also a huge privacy concern ! because a CDN could be spying all the traffic of every single pages of your websites (where the CDN is added) via the
Refererheader ! They could also see theUserAgentof every visitors. They could estimate how much revenues you make based on how many times your "Payment success" page is called, and so on ! - CDNs sometimes can be slow in an unpredictable way (ex: if their server receive a spike of requests or have network problems, etc). I've personally seen a request taking as long as 8 seconds !! And during that time, the website was not rendering because it was waiting for that dependency to load.
- It's preventing you to work on your website offline when you don't have access to Internet, which is annoying.
