how to install using npm code example

Example 1: install node modules

// Install as a dependency
npm install --save packageName
// OR
npm install --save package1 package2
// OR
npm install --save package@version
// OR
npm i -s packageName

// Install as a dev-dependency
npm install --save-dev package@version
// OR
npm i -D packageName

//Install globally
npm install --global packageName
//OR
npm i -g packageName

// You might need SU access on macos/linux to install globally

Example 2: install node modules from package.json

npm install (with no args, in package dir)
npm install [<@scope>/]<name>
npm install [<@scope>/]<name>@<tag>
npm install [<@scope>/]<name>@<version>
npm install [<@scope>/]<name>@<version range>
npm install <git-host>:<git-user>/<repo-name>
npm install <git repo url>
npm install <tarball file>
npm install <tarball url>
npm install <folder>

aliases: npm i, npm add
common options: [-P|--save-prod|-D|--save-dev|-O|--save-optional] [-E|--save-exact] [-B|--save-bundle] [--no-save] [--dry-run]

Example 3: what is npm install

npm install module-name
npm i module-name
puts module-name package (js library file) 
into node_modules folder
so you can require it in node app