Yarn and npm are two popular package managers for JavaScript that help manage project dependencies, but each has unique features that may suit different project needs.

1. Speed and Performance

Yarn generally offers faster installations because it downloads packages in parallel and uses offline caching, meaning it can pull packages from a local cache instead of redownloading them each time. This caching can save significant time on large projects.
npm has made strides in recent versions (npm 5+), incorporating caching and improving speed, but it still installs packages sequentially, making it typically slower than Yarn, especially for complex projects with many dependencies.

2. Dependency Consistency and Lock Files

Yarn uses yarn.lock to lock package versions, ensuring that installations are consistent across different environments. This file is particularly useful for projects requiring strict version control.
npm introduced a similar package-lock.json file in version 5 to tackle the same issue, allowing for more dependable version management across development environments.

3. Workspaces and Monorepo Support

Yarn includes robust workspace support, making it ideal for monorepo projects where multiple packages need centralized dependency management. This feature helps teams manage large codebases with shared dependencies.
npm introduced workspace support in version 7, narrowing the gap, though Yarn's workspaces remain a preferred choice for larger-scale monorepos due to its longer-established support.

4. Security Checks

npm includes npm audit, which scans for vulnerabilities in dependencies and provides recommendations for fixes. This feature is popular among developers prioritizing security.
Yarn also offers a security check but doesn't provide as detailed insights as npm audit, although both package managers use encryption to verify package integrity.

5. Ease of Use and Commands

Yarn and npm share many similar commands, making it easy to switch between them. For instance, npm install is equivalent to yarn add, and npm uninstall aligns with yarn remove. However, Yarn includes some unique commands, such as yarn why to show package dependencies, which can be helpful for debugging.
For those switching from npm to Yarn, Yarn is compatible with package-lock.json files, allowing easy migration without losing version data.

6. Zero Installs (Yarn Only)

Yarn has a unique "Zero Installs" feature, storing dependencies directly in the project’s directory. This approach allows nearly instant access without an internet connection, which can be especially valuable in distributed environments.

If you prioritize speed, consistency, and monorepo support, Yarn may be the better option, especially for large projects. However, npm offers broader community support and excellent security auditing tools, making it a solid choice for projects needing these features.

Both Yarn and npm are robust and capable. Experimenting with both on different projects might help you decide which one fits your workflow best.

(https://www.sitepoint.com/yarn-vs-npm/), PhoenixNAP, and Toxigon.

Yarn vs Npm