When using npm (Node Package Manager) to install dependencies, the --save flag was used to add the installed package to the dependencies section of the project's package.json file. This ensured that the version and details of any dependency package were recorded, allowing others to install the same version of dependencies when they obtain the project code by running npm install, thus ensuring project consistency and reproducibility.
Starting from npm 5.0, the --save flag is no longer necessary because running npm install <packageName> automatically adds the package to dependencies unless specified otherwise. If you want to add the package to devDependencies (which are typically dependencies for development, such as testing frameworks or build tools), you can use the --save-dev flag.
For example, suppose you are developing a Node.js project and need to install the express library. Before npm 5.0, you would run:
npm install express --save
This command installs express and adds it to the dependencies section of package.json. However, starting from npm 5.0, you can simply run:
npm install express
This automatically saves the dependency to package.json without the need for the --save flag. If express is a library only needed during development (e.g., if it is a testing library), you might want to use:
npm install express --save-dev
This will add express to the devDependencies section of package.json, not to dependencies.
In summary, the --save flag was an important feature of npm for ensuring that project dependencies could be correctly recorded and managed. With the development of npm, this step has been automated, making package management simpler and more direct.