When we imported the jQuery library into our client application, we directly referred to its optimized source from its vendor as <script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.min.js "/>.

Now, imagine that for some reason this site goes down either temporarily or for good; this will make our application unusable, as the import wouldn't work.

Content Delivery Networks come to help in these cases. They serve as a repository for libraries or other static media content, assuring that the needed resources will be available without downtime, even when something goes wrong with their vendors. One of the most popular JavaScript CDNs is https://cdnjs.com/; it provides the most common JS libraries available out there. We will switch our clients to refer to the jquery library from this CDN rather than from its vendors' website at <script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.min.js "/>.

While there is hardly anything wrong with directly downloading your JS libraries and placing them in the static directory of your node.js project, it may lead to having local changes and fixes directly in your library dependencies. This can easily result in incompatible changes and can prevent your application from easily switching to newer versions in the future. As long as your dependencies are open source, you should strive to improve them by contributing fixes or reporting bugs rather than having fixes in your own local fork. Still, if you are unfortunate enough to run into a bug that you can easily fix, you can fork the library to resolve your problem faster. However, always consider contributing the fix back to the community. After it is accepted, switch back to the official version; otherwise, you will find yourself in a difficult situation the next time with another issue, and the community would track it much harder if reported from a forked version. That is the beauty of open source, and that is why you should always consider consuming JavaScript APIs' Content Delivery Networks. They will provide you with the stability and support you may need at any point in the life of your application.