What is the purpose of the 'node_modules' folder?

What exactly is the node_modules folder and what is it for?

I know when we download any library with npm, the library goes to folder node_modules. I also know that, when we are going to upload it (to GitHub, for example) we have to ignore the node_modules folder, because it takes a lot of space. Through file package.json we can download all dependencies using npm i.

Let's say I want to deploy my app/website to some server/host, do I have to upload the node_modules folder to server as well?

And another thing. Usually, I download my jQuery and Bootstrap files from the website and copy in the content to the css/js folder inside my project, but this time I tried with npm and everything goes to folder node_modules and I'm using Cordova. When I execute the command cordova build, neither my jQuery nor my Bootstrap files are generated.

So those are my questions:

• if I want to host my project, do I really have to upload the node_modules folder as well?
• And when it's Cordova or Ionic, do I also have to copy the node_modules folder to the www folder?
• If so, what is the point of using npm to download libraries? Is this how it's really done? Which one is better? Going to the website, download the file, and paste inside www, or download through npm?

What is the purpose of node_modules folder?

You can think of the node_modules folder like a cache for the external modules that your project depends upon. When you npm install them, they are downloaded from the web and copied into the node_modules folder and Node.js is trained to look for them there when you import them (without a specific path). I refer to it as a cache because the node_modules folder can be entirely recreated from scratch at any time by just reinstalling all the dependent modules (that should be listed in your project folders).

but I know when we are going to upload it to github we have to ignore the node_modules folder because it takes a lot of space.

This is because there's no reason to store copies of all your dependent modules in your own GitHub project. The exact version you were using is known and stored in your package.json or package-lock.json so at any time you or anyone else using your project can download your code and then fetch all the other dependent modules from their original source (including even the exact same versions you were using). So, there isn't any reason to store a separate duplicate copy of all those dependent modules in your own project. That would just be wasteful and would complicate upgrading to a newer version of all those dependent modules.

So that's my question, if I want to host my project, Do I really have to upload the node_modules as well?

If you have your project running on your local machine and you now want to move it to your hosting location, it is best to reinstall all the dependent modules on the hosting machine and not copy them from your development machine. This is because the process of installing them on the hosting machine (which might be a different platform or OS than your development machine) may use a bit of a different install process for the specific hosting environment.

What exactly is the node_modules folder and what is it for?

It just a directory created by npm and a way of tracking each packages you install locally via package.json. If you had tried deleting the node_module folder and ran the application, you would get Error:Cannot find module 'some-module/methods'. That basically means that your machine would complain that you are using some module, but but the machine is unable to locate it.

And personally I would not recommend directly editing the node_modules folder if you're going to explore it's functionalities. Ideally you should fork the repo for edits, compilation and execution before pushing it back to your repo. Usually editing the node_modules can overwrite all changes when npm install is used and as a result, nobody would be able to clone your repo since you can't add node_modules into github.

. . .

Let's say I want to deploy my app/website to some server/host, do I have to upload the node_modules folder to server as well?

Strongly advise you to avoid uploading the node_modules folder to server manually. Doing this can kill your version dependencies. To re-iterate my point, node_modules is just an external directory that is created by npm install easily. If you are going to deploy your app to another server, the node_modules are easily available to be installed separately. So move all your files except the node_modules folder to the server and run npm install before executing the application.