自动更新package.json中的依赖项

Question

I have one question I think is pretty simple. Could you explain me why sometimes package.json is automatically updates and sometimes don't. eg if I installed express or gulp these plugins were added to dependencies automatically. But if I installed express-jwt or mongodb these plugins were not added

Answer 1

They are added to package.json when you append one of the following flags:

-S|--save|-D|--save-dev|-O|--save-optional

See https://docs.npmjs.com/cli/install for full documentation.

Answer 2

When you install a package with the --save or --save-dev flag, these are persisted to the dependencies or devDependencies arrays respectively.

If no flag is added, the package is downloaded but not persisted to package.json

Edit: There's is also the more obscure --save-optional flag, but it'd say it's mostly out of scope for this particular case.

Answer 3

If we use the following command to install npm dependencies-

npm install express-jwt --save or npm install mongodb --save

these installed dependencies will also be added to package.json file.