If you're running into compatibility issues with peer dependencies in your project, consider using the flag --legacy-peer-deps.

Peer dependencies allow packages to rely on one another without being direct dependencies, reducing redundancy in your project. However, if you encounter conflicts with peer dependencies, the --legacy-peer-deps option can help by instructing npm or Yarn to take a more forgiving approach when resolving and installing packages.

This flag is particularly handy when dealing with older packages that may not have updated their peer dependency definitions to work seamlessly with newer package manager behavior.

npm install --legacy-peer-deps

To better understand the issue at hand, let's delve into the error message:

npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: <a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="f080829f9a959384dd91949d999eb0c1c1dec0dec0">[email protected]</a>
npm ERR! Found: @angular/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="6a0905070705042a5b5b445a4459">[email protected]</a>
npm ERR! node_modules/@angular/common
npm ERR!   @angular/common@"11.0.3" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer @angular/common@"^9.1.0 || ^10.0.0" from @agm/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="a0c3cfd2c5e0938e908e908dc2c5d4c18e90">[email protected]</a>
npm ERR! node_modules/@agm/core
npm ERR!   @agm/core@"3.0.0-beta.0" from the root project

The key is to analyze the problem starting from the bottom up. It appears that @agm/[email protected] requires either angular common version 9.1.0 or 10.0.0. However, the currently detected angular common version is actually 11.0.3.

(For a clearer understanding of dependencies, check out this simple site: How npm3 Works)

dependencies — these are the essential dependencies that you rely on and call in your project’s code
devDependencies — these are your development dependencies, for example, a prettier library for formatting code
peerDependencies — if you set a peer dependency in your package.json, you are telling the person who installs your package that they need that dependency with the specified version
optionalDependencies — these dependencies are optional and failing to install them will not break the installation process
bundledDependencies — it’s an array of packages that will come bundled with your package. This is useful when some 3rd party library is not on NPM, or you want to include some of your projects as modules

So what's the solution? The core issue lies within the peer dependencies. To resolve this, you can either downgrade angular common or utilize legacy dependencies logic by using --legacy-peer-deps flag during package installation. Enabling --legacy-peer-deps prevents automatic installation of peerDependencies. Will this fix your problem? Most likely yes, but specific instructions should be given on how to proceed. Alternatively, you can make use of the following command mentioned in a previous answer:

npm config set legacy-peer-deps true

In my personal experience, without setting the configuration above, I encountered missing dependency packages while running ng serve due to --legacy-peer-deps usage. I had to manually install those missing packages. After installing approximately five packages manually with --legacy-peer-deps, there was one package that could not be installed, leading me to abandon its use and seek an alternative.

Other potential solutions I came across include:

• Downgrading Node.js to v14 to also downgrade npm, which seemed to assist many users.
• Using Yarn to enforce package installation - although unfamiliar with the process myself.
• Lowering the versions of Angular and global Angular CLI to fulfill requirements.
• Exploring if updating all packages using helps, especially for new projects.

Aside from utilizing the --legacy-peer-deps flag in the command line, you can also establish this as a long-term configuration setting:

npm config set legacy-peer-deps true

When utilizing npm version 7, encountering peer dependency issues as errors is a common occurrence, unlike in version 6 where they were typically just warnings. In most cases, adding --legacy-peer-deps can resolve the issue with npm 7.

If this solution does not yield results, one alternative is to revert back to npm 6. It is not necessary to downgrade Node.js, although it is also harmless to do so. The key code for managing dependencies lies within npm. Reverting Node.js might inadvertently address the problem as it often leads to a downgrade of npm as well.

An option that is less invasive than downgrading npm involves using npx to execute the previous version of

npm</code solely for the installation command: <code>npx -p npm@6 npm install

In cases of complete failure, it may be beneficial to delete the node_modules directory and package-lock.json, followed by running npm install again. This process will regenerate both node_modules and package-lock.json.

To begin, run the following command in your terminal.

npm config set legacy-peer-deps true

Next, ensure to clear the cache:

npm cache clean --force

Lastly, proceed with executing your desired command.

If you've recently updated to npm 7, you may encounter issues with certain packages.

Using the --legacy-peer-deps parameter can provide a solution:

npm i --legacy-peer-deps

More information can be found here: legacy-peer-deps

This instructs npm to disregard peerDependencies completely during package tree construction, similar to versions 3 through 6 of npm.

If there are conflicts due to strict peerDependencies preventing installation of a package, this option allows for progression in resolving the issue. ...

You also have the choice to set this option to true by default, although it is not recommended by npm:

npm config set legacy-peer-deps true

Alternatively, you can choose to wait until these packages are updated.

The issue at hand stems from a conflict in dependencies or a malfunctioning dependency. To move forward, you'll need to accept the discrepancy in the dependency and proceed with a forced installation.

Resolution: Execute the following command using --force.

Run the command as follows:

npm install --force @your-npm-package

.

Note: If feasible, consider using the yarn package manager for installing the dependency.

NPM is a powerful tool for installing and managing dependencies in your projects.

I encountered a similar issue with React versions and npm:

Error message: types/[email protected]

This could be due to specific package versions that need to be installed as per your package.json file.

Issues may arise with npm version 7, making it unable to install Node.js modules.

By downgrading npm to version 6, these errors can turn into warnings and the problem can be fixed.

• Try running this command: npm install -g npm@6

• Check if the desired version is already installed: npm --version

• To remove and re-install node_modules package:

  a) Remove using rm -rf node_modules

  b) Reinstall: npm i

Important Note: Please ensure that you are using npm version 7 or newer

Take heed: If you opt to follow the advice given by other commenters, it will result in a user-specific configuration that may not synchronize consistently across team members, various devices, or build environments.

Coping with Outdated Peer Dependencies on a Project Level

If you prefer having legacy-peer-deps tied to your current project, ensuring its uniformity across different setups and avoiding interference with other projects is crucial.

npm config set legacy-peer-deps true --location project

This action generates a local file named .npmrc, which can be included in your repository:

legacy-peer-deps=true

Simply execute:

npm install

Subsequently, commit the updated lockfile.

It's essential to bear in mind the significance of correct location settings:

• Project-Specific Configuration (/path/to/my/project/.npmrc, learn more here):

  npm config set legacy-peer-deps true --location project
  

• User-Based Configuration (defaults to $HOME/.npmrc, further details)

  npm config set legacy-peer-deps true --location user
  

  Suitable alternative - default setup targets user-based configuration anyway:

  npm config set legacy-peer-deps true
  

• Universal Configuration (typically relies on $PREFIX/etc/npmrc, explore further)

  npm config set legacy-peer-deps true --location global
  

  Alternatively, utilizing --global implies --location global

  npm config set legacy-peer-deps true --global
  

Adapting Dependencies for Complex Projects

In my experience, a critical dependency with an outdated version insists on incorporating webpack v3 (!) - despite being a necessary component for that specific project.

An interim measure would involve leveraging legacy-peer-deps as a temporary solution.

In situations of dire need, contemplating a fork of the dependency with adjusted peer dependencies to align with your requirements could also be considered - subsequently directing your project to this modified version.

To resolve the issue, consider deleting the node modules folder and the package-lock.json file before running the command npm install. Alternatively, you can try executing npm cache clean --force

Initially, my approach was

npm install

However, I encountered an issue with the message

unable to resolve dependency tree

. Following the guidance provided by this command,

To fix the conflict in upstream dependencies, either resolve it or retry
npm ERR! running this command with --force, or --legacy-peer-deps
npm ERR! to accept a potentially incorrect (and broken) resolution of dependencies.

In response, I executed the following:

npm install --legacy-peer-deps

Surprisingly, this action successfully resolved my problem.

Here are two possible solutions to fix the issue at hand:

• Solution 1: Begin by deleting the node_modules folder and the file package_lock.json. Then, execute the following commands:

  npm cache clean --force after npm i --force

• Solution 2: Simply run

  npm install --save --legacy-peer-deps

To address the error message indicating an ERESOLVE issue with resolving dependency tree during package installation, consider implementing one of the following solutions:

1. Opt for installing the package through npm install command while including --legacy-peer-deps flag

   npm install --save --legacy-peer-deps
   

2. Alternatively, follow this two-step process:

   a. Enable legacy-peer-deps setting in npm config

   npm config set legacy-peer-deps true
   

   b. Proceed to install the packages using npm install

   npm install
   

The quickest fix: npm install --legacy-peer-deps

Explanation:

Prior to npm version 7, peerDependencies had to be manually installed or they would trigger a warning if an incompatible version was detected in the dependency tree. With npm v7, peerDependencies are now automatically installed.

npm documentation on peerDependencies

Your package has some peerDependencies that clash with the dependencies of the main project.

This is evident from the npm ERR message log.

The issue at hand is that gf-kautomata-pipeline-ui is utilizing Angular 9, while @angular/http necessitates Angular 7. (Note that @angular/http has been deprecated and its functionalities have been integrated into @angular/common.)

For more information visit: https://www.npmjs.com/package/@angular/http

If you are working with Angular 9:

1. Remove @angular/http from your package.json (It is not required in Angular 9)

2. Ensure that @angular/common is present in your package.json.

3. Execute the command npm i.

If you are using Angular 7, review your package.json to confirm that all Angular packages do not exceed ^7.0.0. You may also need to eliminate gf-kautomata-pipeline-ui, or reach out to the creator of gf-kautomata-pipeline-ui to determine its compatibility with Angular 7.

Many responses here suggest two possible solutions:

npm i --force

and

npm i -legacy-peer-deps

These are considered quick fixes, but let's delve deeper into what they actually do.

When you use the npm i --force command with Node Package Manager (npm), it forcefully installs packages. This means npm will install the specified packages even if they are not compatible with your current project version or if conflicts with other dependencies arise.

On the other hand, npm i --legacy-peer-deps tells npm to use an older algorithm for resolving peer dependencies, similar to how it was done in older versions of npm before version 5. This can be useful when certain packages have not been updated to comply with newer peer dependency rules introduced in npm 5. However, this issue may persist in your project, necessitating using either --force or -legacy-peer-deps every time you install another package.

It is worth mentioning that both of these options are not recommended unless there are no better alternatives available.

Though I have used these methods in many projects, recently I tried a different approach. Let me share what worked for me.

1. Delete the node_modules folder and package-lock.json.
2. Run npm cache clean --force.
3. Make note of all the packages listed in package.json.
4. Delete the dependencies from package.json.
5. Manually install all dependencies using npm i package1 package2.
6. Address any version upgrade issues that may arise to resolve the problem.

After upgrading from npm version 6 to 7, I encountered an error message (shown below).

npm ERR! code ERESOLVE npm ERR! ERESOLVE unable to resolve dependency tree

...

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

Trying to compile with either the --legacy-peer-deps or --force flags led to a problematic bundle for me.

To address this issue, I decided to delete the node_modules, package-lock.json, and then bundled using yarn install. This approach generated a new yarn.lock file and a functioning package-lock.json that worked well during subsequent npm runs.

Note: I am currently utilizing this temporary solution until npm 7 is fully compatible with my project. Once it is, I plan to remove the yarn.lock, package-lock.json, as well as the node_modules folder, and recompile using npm.

rm -rf node_modules
rm package-lock.json
yarn install
# Generates a yarn.lock file and a new package-lock.json

# Proceed with npm
npm start

After updating my Node.js, everything started working smoothly:

node -v

The result was:

V xxxx

Additionally, I ran the following command to install the stable node release:

sudo npm install -g n

Then, I used this command:

sudo n stable

1. To begin, remove the node_modules folder and package-lock.json file from your root directory:

   rm -r node_modules
   rm package-lock.json
   

2. Next, execute the following commands:

   npm install --save --legacy-peer-deps
   npm audit fix --force
   

3. Make sure to create a .env file in your root directory with the code snippet below:

   SKIP_PREFLIGHT_CHECK=true
   

4. Finally, launch your project by running:

   npm start
   

After encountering this problem repeatedly, I finally discovered a fix:

npm install react-native-paper  --legacy-peer-deps

Try this solution:

npm install --legacy-peer-deps

I successfully resolved my issue using this method.

Kindly use npm install --save --legacy-peer-deps to add the "word" package with Angular 13.

Encountered an error on GitHub actions when trying to push my updated package and package-lock JSON file.

The root of the problem stemmed from inconsistencies within our internal NPM packages. To resolve this issue, I ended up including

legacy-peer-deps=true

within our .npmrc file in order to override the dependency causing the error.

Utilizing legacy-peer-deps at times can be a helpful way to manage unwanted dependencies within your project packages.

After running this command successfully on my MacBook Pro 2016.

npm install --legacy-peer-deps

Followed by:

npm install

During a recent project in Angular 13 utilizing packages from a private npm feed in Azure DevOps, I encountered an issue.

The problem of ERESOLVE unable to resolve dependency tree arose.

To address this issue, I implemented an .npmrc file to access the repository. Subsequently, the npm install command began searching for all packages within my private repository instead of the npm feed as intended. This resulted in the unable to resolve the dependency tree error due to missing packages hosted exclusively on the npm feed and not my private one.

Fortunately, I stumbled upon an insightful solution on how to scope packages.

Following that, I made the following adjustments:

1. In my library's Package.json, I updated the name to include a scoped name @mylib

   "name": "@myLib/command-queue",
   

2. I built and published this package to my private feed

3. In my client app (the one utilizing this package), I modified the .npmrc file to target my private feed specifically for packages under this scope

   @myLib:registry=https://pkgs.dev.azure.com/...
   always-auth=true
   

Now, whenever I execute the command npm install, it will search for packages with the scope @myLib in my private feed, while using the npm feed for all other instances (e.g., @angular/...)

Here is an excerpt from my client app's Package.json file:

    "@angular/platform-browser-dynamic": "~13.3.0",
    "@angular/router": "~13.3.0",        <-- sourced from npm
    "@myLib/jcg-command-queue": "^2.2.0", <-- obtained from my private feed

Furthermore, this adjustment eliminates the necessity of adding --legacy-peer-deps to the npm install command.

We encountered a similar issue, which led to the following error:

npm ERR! code ERESOLVE npm
ERR! ERESOLVE could not resolve npm
ERR! npm
ERR! While resolving: @angular/[email protected] npm
ERR! Found: @angular/[email protected] npm
ERR! node_modules/@angular/material npm
ERR! @angular/material@"~12.0.4" from the root project
...

In our case, we utilize npm ci for a clean install within Azure Pipelines.

The problem often stemmed from discrepancies between the package.json and package-lock.json files.

To address this, we performed a local npm install followed by updating the package-lock.json file before pushing it.

As an additional precautionary measure, we included an extra task in our pipeline to provide more details if the job fails.

- task: Npm@1
   displayName: npm install
   inputs:
     command: custom
     customCommand: ci
     customRegistry: useNpmrc

 # ##vso[task.logissue type=error] writes the text to the summary page (error-log).
 - bash: echo "##vso[task.logissue type=error] If 'npm install' fails with 'ERESOLVE could not resolve', 'package.json' and 'package-lock.json' (needed for 'npm ci') may be out of sync. Run 'npm install' locally and push the new package-lock.json."
   condition: failed() # Only execute on fail
   displayName: npm install failed hint

If you're having trouble updating packages in a legacy project, try resetting the package-lock.json:

git checkout -- package-lock.json

Here's the scoop: I've encountered this issue multiple times when updating all packages in an older project. I strongly advise against using npm audit fix or npm i --force. Simply deleting the package-lock.json doesn't always do the trick. Reverting back to a known good version of both package.json + package-lock.json and then adding packages has consistently been the safest and quickest solution for me.

There was a situation where I encountered similar issues when attempting to either update my current Angular 11.x project created from a previous ng new, or create a new project using Angular 12.x with ng new abc. It turned out that I had overlooked upgrading Angular CLI. Running

npm install -g @angular/cli@latest

resolved the errors I was facing during the creation of the new project.

During my recent experience, I encountered challenges with a crucial dependency known as @babel/core. Although tempted to resort to using --force, I hesitated due to uncertainties regarding potential consequences. Instead, I navigated to https://www.npmjs.com/, located the package in question, and proceeded to upgrade from my outdated version to the latest one. This simple action proved to be effective in resolving the issue at hand.