Why wouldn't you want to use the `--save` option for npm install?

Question

I read about using the --save option here and and it says that it will add the installed package to your package.json file. But why isn't this automatic? Wouldn't you always want this?

My understanding is that the node_modules is the directory that actually holds the code of your package and package.json is the reference/list of all the packages you have installed so that when you push it up to a repo, you only push the latter up and not the former, to save space.

Then when other people clone or fork off your repo, they will have the package.json to reference and install all the necessary packages to work off of your project.

Thus, wouldn't you always want your packages to be in the package.json in order for everyone to get what is needed?

Answer 1

With package managers like Bower or npm, I think --save is not automatic for the following reasons:

1. Not all dependencies are production dependencies (see --save-dev).
2. Sometimes you need to test a package without altering your package.json.
3. You may prefer to install locally some packages that your colleagues installed globally on their computer.

Packages installed without --save are not considered as dependencies and are kept separate. You can detect them easily as extraneous packages with npm ls and remove them instantly with npm prune.

Now if you think extraneous packages are a bad thing, you can of course use --save everytime you install a new package. For practical reasons, be aware that you can use the -S shortcut instead of --save. Moreover, if you often forget to use the option, you could define an alias in your shell.

Finally, if you use Yarn, notice that the yarn add command will add each package as a dependency. No --save flag anymore.