Answer by Selva Ganapathi for What's the difference between dependencies, devDependencies, and peerDependencies in NPM package.json file?

Dependencies vs dev dependencies

Dev dependencies are modules which are only required during development whereas dependencies are required at runtime. If you are deploying your application, dependencies has to be installed, or else your app simply will not work. Libraries that you call from your code that enables the program to run can be considered as dependencies.

Eg- React , React - dom

Dev dependency modules need not be installed in the production server since you are not gonna develop in that machine .compilers that covert your code to javascript , test frameworks and document generators can be considered as dev-dependencies since they are only required during development .

Eg- ESLint , Babel , webpack

@FYI,

mod-a  dev-dependents:    - mod-b  dependents:    - mod-cmod-d  dev-dependents:    - mod-e  dependents:    - mod-a----npm install mod-dinstalled modules:  - mod-d  - mod-a  - mod-c----checkout the mod-d code repositorynpm installinstalled modules:  - mod-a  - mod-c  - mod-e

If you are publishing to npm, then it is important that you use the correct flag for the correct modules. If it is something that your npm module needs to function, then use the "--save" flag to save the module as a dependency. If it is something that your module doesn't need to function but it is needed for testing, then use the "--save-dev" flag.

# For dependent modulesnpm install dependent-module --save# For dev-dependent modulesnpm install development-module --save-dev