What is the difference between --save and --save-dev?

Question

What is the difference between:

npm install [package_name]

and:

npm install [package_name] --save

and:

Answer 1

You generally don't want to bloat production package with things that you only intend to use for Development purposes.

Use --save-dev (or -D) option to separate packages such as Unit Test frameworks (jest, jasmine, mocha, chai, etc.)

Any other packages that your app needs for Production, should be installed using --save (or -S).

npm install --save lodash       //prod dependency
npm install -S moment           // "       "
npm install -S opentracing      // "       "

npm install -D jest                 //dev only dependency
npm install --save-dev typescript   //dev only dependency

If you open the package.json file then you will see these entries listed under two different sections:

"dependencies": {
  "lodash": "4.x",
  "moment": "2.x",
  "opentracing": "^0.14.1"
},

"devDependencies": {
    "jest": "22.x",
    "typescript": "^2.8.3"
},