What is the --save option for npm install?

Update npm 5:

As of npm 5.0.0, installed modules are added as a dependency by default, so the --save option is no longer needed. The other save options still exist and are listed in the documentation for npm install.

Original answer:

Before version 5, NPM simply installed a package under node_modules by default. When you were trying to install dependencies for your app/module, you would need to first install them, and then add them (along with the appropriate version number) to the dependencies section of your package.json.

The --save option instructed NPM to include the package inside of the dependencies section of your package.json automatically, thus saving you an additional step.

In addition, there are the complementary options --save-dev and --save-optional which save the package under devDependencies and optionalDependencies, respectively. This is useful when installing development-only packages, like grunt or your testing library.

Update as of npm 5:

As of npm 5.0.0 (released in May 2017), installed modules are added as a dependency by default, so the --save option is no longer needed.
The other save options still exist and are listed in the documentation for npm install.

Original Answer:

To add package in dependencies:

npm install my_dep --save

or

npm install my_dep -S

or

npm i my_dep -S

To add package in devDependencies

npm install my_test_framework --save-dev

or

npm install my_test_framework -D

or

npm i my_test_framework -D

package.json

Update as of npm 5:

As of npm 5.0.0, installed modules are added as a dependency by default, so the --save option is no longer needed. The other save options still exist and are listed in the documentation for npm install.

Original answer:

It won't do anything if you don't have a package.json file. Start by running npm init to create one. Then calls to npm install --save or npm install --save-dev or npm install --save-optional will update the package.json to list your dependencies.

According to NPM Doc:

So it seems that by running npm install package_name, the package dependency should be automatically added to package.json, right?

You can also use -S, -D or -P which are equivalent of saving the package to an application dependency, a development dependency or production dependency. See more NPM shortcuts below:

-v: --version
-h, -?, --help, -H: --usage
-s, --silent: --loglevel silent
-q, --quiet: --loglevel warn
-d: --loglevel info
-dd, --verbose: --loglevel verbose
-ddd: --loglevel silly
-g: --global
-C: --prefix
-l: --long
-m: --message
-p, --porcelain: --parseable
-reg: --registry
-f: --force
-desc: --description
-S: --save
-P: --save-prod
-D: --save-dev
-O: --save-optional
-B: --save-bundle
-E: --save-exact
-y: --yes
-n: --yes false
ll and la commands: ls --long

This list of shortcuts can be obtained by running the following command:

npm help 7 config

npm v6.x update

Now you can use one of npm i or npm i -S or npm i -P to install and save a module as a dependency.

npm i is the alias of npm install

1. npm i is equal to npm install, meaning the default save module as a dependency;
2. npm i -S is equal to npm install --save (npm v5-)
3. npm i -P is equal to npm install --save-prod (npm v5+)

Check out your npm version

npm -v

6.14.4

Get npm cli help information

npm -h

Usage: npm <command>

where <command> is one of:
    access, adduser, audit, bin, bugs, c, cache, ci, cit,
    clean-install, clean-install-test, completion, config,
    create, ddp, dedupe, deprecate, dist-tag, docs, doctor,
    edit, explore, fund, get, help, help-search, hook, i, init,
    install, install-ci-test, install-test, it, link, list, ln,
    login, logout, ls, org, outdated, owner, pack, ping, prefix,
    profile, prune, publish, rb, rebuild, repo, restart, root,
    run, run-script, s, se, search, set, shrinkwrap, star,
    stars, start, stop, t, team, test, token, tst, un,
    uninstall, unpublish, unstar, up, update, v, version, view,
    whoami

npm <command> -h  quick help on <command>
npm -l            display full usage info
npm help <term>   search for help on <term>
npm help npm      involved overview

Specify configs in the ini-formatted file:
    /Users/xgqfrms-mbp/.npmrc
or on the command line via: npm <command> --key value
Config info can be viewed via: npm help config

npm@6.14.4 /Users/xgqfrms-mbp/.nvm/versions/node/v12.18.0/lib/node_modules/npm

Get npm install help

npm help install alias npm -h i

npm help install

# OR, alias
npm -h i

Output:

npm install (with no args, in package dir)
npm install [<@scope>/]<pkg>
npm install [<@scope>/]<pkg>@<tag>
npm install [<@scope>/]<pkg>@<version>
npm install [<@scope>/]<pkg>@<version range>
npm install <alias>@npm:<name>
npm install <folder>
npm install <tarball file>
npm install <tarball url>
npm install <git:// url>
npm install <github username>/<github project>

aliases: i, isntall, add
common options: [--save-prod|--save-dev|--save-optional] [--save-exact] [--no-save]
➜  ~

References

npm-install

Use:

npm install package_x --save

The given package (package_x) will be saved in file package.json inside dependencies.

If you add

npm install <<package_x>> --save-dev

then it will be saved inside devDependencies.

As of npm 5, it is more favorable to use --save-prod (or -P) than --save but doing the same thing, as is stated in npm install. So far, --save still works if provided.

As of npm 5, npm will now save by default.

In case, if you would like npm to work in a similar old fashion (no autosave) to how it was working in previous versions, you can update the config option to enable autosave as below.

npm config set save false

To get the current setting, you can execute the following command:

npm config get save

Source: Here’s what you need to know about npm 5

–npm install --save or -S: When the following command is used with npm install, this will save all your installed core packages into the dependency section in the package.json file. Core dependencies are those packages without which your application will not give the desired results.

But as mentioned earlier, it is an unnecessary feature in the npm 5.0.0 version onwards.

npm install --save

npm install --save or npm install --save-dev is why we choose one option between these two, while installing the package in our project.

Things are clear from the previous answers that npm install --save will add an entry in the dependency field in the package.json file and other one in dev-dependency.

So the question arises: Why do we need an entry of our installing module in package.json file, because whenever we check in code in Git or giving our code to someone, we always give it or check it without the node_modules folder, because it is very large in size and is also available at a common place, so to avoid this, we do that.

So then how another person will get all the modules that is specifically or needed for that project so answers is from the package.json file that have the entry of all the required packages for running or developing that project.

So after getting the code we simply need to run the npm install command. It will read the package.json file and install the necessary required packages.

The easier (and more awesome) way to add dependencies to your package.json is to do so from the command line, flagging the npm install command with either --save or --save-dev, depending on how you'd like to use that dependency.

npm i (Package name) --save

Simply, using the above command we’ll not need to write the package name in your package.json file, it’ll auto add its name and dependency with version that you’ll need at time when you go for production or set up another time.

npm help install

The above command will help to find out more options and correct def.shown in the picture:

When you are using --save in the npm command to install a package, this means that your project will install those dependencies in the production environment, for example, if you install a library to manage dates.

npm install moment --save
npm i moment -S (same result)

(this is for a production environment)

npm install moment --save--dev
npm i moment -D (same result)

(this is for a development environment)