How to Fix The NPM Conflicting Peer Dependency Error

When working with npm (Node Package Manager), you might encounter a conflicting peer dependency error. This error usually occurs when different packages you’re trying to install depend on different (and often incompatible) versions of the same dependency.

Here's how you can address this issue:

1. Understand Peer Dependencies

Peer dependencies are a way for a package to declare that it expects another package to be present in the consuming project, but it doesn’t install it automatically. It’s the responsibility of the project that uses these packages to ensure the correct version is installed.

For example, if package A requires react@17 and package B requires react@18, npm will throw a conflicting peer dependency error because it’s impossible to satisfy both requests.

Reed also - How Peer Dependencies Work and Why You Need Them.

2. Analyze the Error Message

When npm shows a conflicting peer dependency error, it will usually show which packages are causing the conflict. Here’s an example of what the error might look like:

1 npm ERR! Could not resolve dependency:
2 npm ERR! peer react@"^17.0.0" from package-a@1.0.0
3 npm ERR! node_modules/package-a
4 npm ERR!   package-a@"^1.0.0" from the root project
5 npm ERR!
6 npm ERR! Conflicting peer dependency: react@17.0.0
7 npm ERR!   peer react@"^17.0.0" from package-b@1.0.0
8 npm ERR!   node_modules/package-b
9 npm ERR!     package-b@"^1.0.0" from the root project

In this example, package-a requires react@17, but package-b requires react@18. This conflict prevents npm from resolving the dependencies automatically.

3. Use the --legacy-peer-deps Flag (Quick Fix)

If you're in a hurry and you just want to bypass the conflict, you can use the --legacy-peer-deps flag. This will make npm use the old method of resolving dependencies (used in npm v6 and earlier).

This option tells npm to ignore peer dependency conflicts, allowing you to install the packages without the error. However, this is not a permanent solution and may cause issues in the future because it doesn’t actually resolve the underlying dependency problem.

4. Use --force (Temporary Fix)

Another approach is using the --force flag to force the installation of dependencies, even when there are conflicts.

This is more aggressive than --legacy-peer-deps and could result in broken or incompatible packages. Only use this as a last resort when you're aware of the potential risks.

5. Manually Resolve Peer Dependency Versions (Best Practice)

The best way to solve peer dependency conflicts is by manually updating the version of the conflicting dependencies in your package.json.

Steps:

• 1. Identify the conflicting dependencies from the error message.
• 1. Check the required versions by looking at the peer dependencies of the conflicting packages. For example, if package-a requires react@^17 and package-b requires react@^18, you may need to update one of the packages or find a version of React that works with both.
• 1. Install the correct version of the dependency that satisfies both packages.

For example, if react@18 works with both package-a and package-b:

• 1. Add resolutions in package.json: If you cannot find a version that works for both packages, you can use the resolutions field (if using npm v7+ or yarn). This forces npm or yarn to install a specific version of the dependency.

In package.json, add:

1 {
2   "resolutions": {
3     "react": "18.2.0"
4   }
5 }

Then run:

Note: Using resolutions is a workaround, so be cautious. It could cause breakage if a package requires a strict version.

6. Use npm info to Check Package Versions

You can use the npm info command to inspect which versions of a package are compatible with another package. This will help you determine the versions that satisfy the peer dependencies.

For example, to check the available versions of react:

You can also check the peer dependencies of a specific package:

7. Use npx to Check Dependency Trees

To understand the dependency tree and where the conflicts are happening, you can use the npx npm-why package. It shows why certain packages are installed, which can help you trace the source of peer dependency issues.

1. Install npm-why:

1. Run the tool:

This will show you which packages depend on react and their versions, helping you track down conflicting versions.

Conclusion

To fix npm conflicting peer dependency errors:

• Use --legacy-peer-deps or --force as quick fixes.
• Manually resolve version conflicts for a more permanent solution.
• Use npm info and tools like npm-why to inspect dependencies and understand the conflicts. By carefully resolving dependencies and keeping packages up to date, you can avoid peer dependency conflicts in the future.