--save-dev function is not installed locally in your project.
There are two types of packages.
1) Those who are required to make your project work.
2) Those that are required for the development of your project.
If another developer wants to just use your module (project), he is not interested in installing the development dependencies.
On the other hand, if you want to modify your project, you must install the development dependencies.
That's why a
sass is not installed with
--save so that in
package.json is added in
dependencies , but it must be installed as dependent on development with
--saveDev and it will be added in
In my opinion, copying and pasting
node_modules is a very bad practice, due to the issue of the versions of the packages.