Fix the upstream dependency conflict installing NPM packages

# Fix the upstream dependency conflict installing NPM packages

Use the --legacy-peer-deps flag to solve the npm error "Fix the upstream dependency conflict, or retry this command with --force or --legacy-peer-deps", e.g. npm install --legacy-peer-deps.

The flag causes NPM to ignore peer dependencies and proceed with the installation anyway.

Copied!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.

npm WARN ERESOLVE overriding peer dependency
npm WARN Could not resolve dependency:
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.

Try to run the npm install command with the --legacy-peer-deps flag.

Copied!
npm install --legacy-peer-deps

# 👇️ or use the --force flag
npm install --force

If you got the error when installing a specific module, add the --legacy-peer-deps flag at the end of the command.

Copied!
npm install react --legacy-peer-deps

# 👇️ or use the --force flag
npm install react --force

# Setting the legacy-peer-deps behavior globally

An alternative to setting the legacy-peer-deps flag for every command, is to set the behavior globally with the npm config set command.

Copied!
npm config set legacy-peer-deps true

Starting with NPM v7, NPM installs peerDependencies by default. If you already have a peer dependency of the module installed, but not one of the specified by the module versions, NPM throws an error.

This was the default behavior in NPM versions 4 through 6.

In other words, NPM modules name specific versions of their peerDependencies.

If you have a different version of a peer dependency package installed, an error is raised unless you set the --legacy-peer-deps flag.

# Delete your node_modules and reinstall your dependencies

If the error persists, try to delete your node_modules and package-lock.json (not package.json) files, re-run npm install.

Copied!
# 👇️  (macOS/Linux) delete node_modules and package-lock.json
rm -rf node_modules
rm -f package-lock.json

# 👇️  (Windows) delete node_modules and package-lock.json
rd /s /q "node_modules"
del package-lock.json

# 👇️ clean your npm cache
npm cache clean --force

# 👇️ install packages
npm install

# 👇️ if you get an error, try with `--legacy-peer-deps`
npm install --legacy-peer-deps

Your error message should contain information about which dependency could not be resolved.

Copied!
npm ERR! Could not resolve dependency:
# 👇️
npm ERR! peer react@">=17.0.1" from react-native-web@0.17.1
npm ERR! node_modules/react-native-web
npm ERR!   react-native-web@"^0.17.1" from the root project

You can use the following command to install a specific version of a package.

Copied!
npm install react@17.0.1

And then, you can try to rerun your original npm install command.

# Try to upgrade your version of NPM

Another thing you can try is to upgrade your version of NPM.

Copied!
npm install -g npm@latest

# 👇️ If you get a permissions error on macOS / Linux
sudo npm install -g npm@latest

If you get a permissions error on Windows, open CMD as an administrator and rerun the command.

To open CMD as an administrator:

1. Click on the Search bar and type CMD.

2. Right-click on the Command Prompt application and click "Run as administrator".

3. Rerun the command.

Copied!
npm install -g npm@latest

npm install -g npm@latest --force

# Try updating your NPM packages

The npm audit fix command scans your project for vulnerabilities and automatically installs compatible updates to vulnerable dependencies.

The npm audit fix --force command installs major updates to top-level dependencies, which might introduce breaking changes to your project if you rely on older package versions.

Copied!
npm install --legacy-peer-deps

npm audit fix --force

Try to restart your terminal and development server after running the commands.

If the error persists, try running the npm update command.

Copied!
npm update

# Delete your node_modules and reinstall your dependencies

If you still get an error, try to delete your node_modules and package-lock.json, rerun the npm install command and restart your development server.

Copied!
# 👇️  (macOS/Linux) delete node_modules and package-lock.json
rm -rf node_modules
rm -f package-lock.json
rm -f yarn.lock

# 👇️  (Windows) delete node_modules and package-lock.json
rd /s /q "node_modules"
del package-lock.json
del -f yarn.lock

# 👇️ clean npm cache
npm cache clean --force

# 👇️ install packages
npm install

# 👇️ if you get an error, try with `--legacy-peer-deps`
npm install --legacy-peer-deps

If the error persists, try to use the --force flag.

Copied!
# 👇️ install all using --force
npm install --force

# 👇️ install specific package using --force
npm install react --force

The --legacy-peer-deps flag ignores all peer dependencies when installing (in the style on npm version 4 through 6).

Whereas, the --force flag forces NPM to fetch remote resources even if a local copy exists on disk.