Great questions—let’s walk through both scenarios clearly:

1. Do I need to reinstall a package if I accidentally installed it as a dependency instead of devDependency? #

Short answer: No, you don’t have to reinstall it—but you do need to correct its classification to avoid unnecessary bloat in production builds.

Here’s the breakdown:

• dependencies are packages your app requires to run in production (like express, react, or database drivers)
• devDependencies are only for development workflows (type definitions, linters, bundlers, testing libraries)

If you’ve misclassified a package, two valid approaches work:

• Manual edit: Move the package entry from dependencies to devDependencies in your package.json, then run npm install (or yarn install) to update your lock file and sync the dependency tree.
• Reinstall (optional): Uninstall the package with npm uninstall <package-name>, then reinstall it with npm install <package-name> --save-dev (or yarn add <package-name> --dev). This is more verbose but ensures everything is cleanly registered.

Either method works—pick whichever feels more straightforward for you.

2. Fixing @types/express misclassified as a dependency #

For your specific case with @types/express: you absolutely don’t need to reinstall—just manually move the entry to devDependencies.

Type definition packages (@types/*) are explicitly meant for development only (they don’t contribute to your production code). Here’s the quick fix:

1. Open your package.json
2. Cut "@types/express": "^4.11.1" from the dependencies object
3. Paste it into the devDependencies object (so your devDependencies is no longer empty)
4. Run npm install (or yarn install) to update your lock file

That’s it! Your dependency tree will reflect the correct classification, and you won’t waste time reinstalling the package unnecessarily.

内容的提问来源于stack exchange，提问作者MWN