Specifying an unused dependency in package.json may make packages harder to install. The unused dependency will still be downloaded by npm, and if it conflicts with another package installation will become difficult or impossible.

Dependencies on packages that are only used during development (such as testing frameworks or linters) should be listed under devDependencies rather than dependencies, since they are not required for deployment.

Remove the unused dependency.

In the following example, the package.json file specifies dependencies on both acorn and esprima, but in fact only acorn is used. The dependency on esprima can simply be removed.

As another example, the following package.json file specifies a dependency on eslint-plugin-babel, a plugin for a popular linter:

{ "name": "another-example-package", "version": "0.1.0", "dependencies": { "eslint-plugin-babel": "3.3.0" } }

Since this dependency is only used during development, it should instead be listed under devDependencies:

{ "name": "another-example-package", "version": "0.1.0", "devDependencies": { "eslint-plugin-babel": "3.3.0" } }

NPM Manual: package.json.