npm vs Yarn: choose one and stick with it

I recently watched a tutorial on YouTube where the developer said something along the lines of: "You can install the package with npm. If it doesn't work — use Yarn."

I wanted to scream: That's not how it works!

If you have an existing codebase, you should use the package manager that was used to install the packages in the first place.

npm and Yarn are both package managers for JavaScript, but they are different in numerous ways:

1. Lockfiles and Dependency Resolution

One of the most critical differences between npm and Yarn lies in how they handle dependency resolution and lockfiles.

• npm uses a package-lock.json file to lock dependency versions.
• Yarn uses a yarn.lock file.

If you switch between npm and Yarn in the same project, you might end up with two lockfiles — and worse, an unpredictable build.

2. Performance

Historically, Yarn was created by Facebook to address some pain points in npm v4 and below — especially around speed and reliability.

For a while, Yarn was significantly faster due to its offline cache and parallel installation mechanism. However, npm has since caught up, particularly since v7+, offering better performance and even native support for workspaces.

3. Workspaces and Monorepo Support

Both package managers now support workspaces, which allow you to manage monorepos more easily. However:

• Yarn introduced workspaces first, and their implementation is more mature.
• npm added workspace support starting in v7, but with some limitations compared to Yarn.

If you're using advanced tooling like Yarn Plug'n'Play (PnP), it’s especially important to stick with Yarn — npm has no equivalent for PnP.

4. CLI and Syntax Differences

Though many commands are similar, there are differences:

• npm install installs dependencies.
• yarn or yarn install does the same — but with different defaults and output.

Installing a package:

• npm: npm install react
• Yarn: yarn add react

5. Security and Audit Tools

• npm has a built-in npm audit feature for checking vulnerabilities in your dependencies.
• Yarn also supports auditing via yarn audit, hooking into the same vulnerability database.

However, results might vary, and some teams still prefer npm’s audit tools for their integrations and output.

🚫 So… Don't Switch Package Managers Mid-Project

Switching between npm and Yarn without a clear reason — and without reinitializing the lockfile — is risky.

If your repo has a yarn.lock, use Yarn.
If it has a package-lock.json, use npm.

It's not about which is better — it's about consistency.

Doing otherwise isn’t just a “wrong command.” It’s potentially introducing bugs and instability into your application, especially in production environments.