Yarn vs NPM

If you use nodejs you probably used npm before.
Yarn is something similar, It is another package manager like npm.
NPM and Yarn are package managers that help to manage a project’s dependencies. A dependency is, as it sounds, something that a project depends on, a piece of code that is required to make the project work properly. We need them because managing the project’s dependencies is a difficult task and it quickly becomes tedious, and out of hand when the project grows. By managing the dependencies, we mean to include, un-include, and update them.

npm: It is the default package manager for the JavaScript runtime environment Node.js. It consists of a command-line client, also called npm, and an online database of public and paid-for private packages called the npm registry.

yarn: It stands for Yet Another Resource Negotiator and it is a package manager just like npm. It was developed by Facebook and is now open-source. The intention behind developing yarn(at that time) was to fix performance and security concerns with npm.

The differences between npm and yarn are explained below:

Installation procedure

npm: npm is installed with Node automatically.
yarn: To install yarn npm have to be installed.
npm install yarn --global
The lock file

npm: NPM generates a ‘package-lock.json’ file. The package-lock.json file is a little more complex due to a trade-off between determinism and simplicity. Due to this complexity, the package-lock will generate the same node_modules folder for different npm versions. Every dependency will have an exact version number associated with it in the package-lock file.
yarn: Yarn generates a ‘yarn.lock’ file. Yarn lock files help in easy merge. The merges are predictable as well, because of the design of the lock file.
Installing global dependencies

npm: To install a global package, the command template for npm is:
npm install -g package_name@version_number
yarn: To install a global package, the command template for yarn is:
yarn global add package_name@version_number

License Checker

npm: npm doesn’t has a license checker that can give a handy description of all the licenses that a project is bound with, due to installed dependencies.
yarn: Yarn has a neat license checker. To see them, run
yarn licenses list

Fetching packages

npm: npm fetches dependencies from the npm registry during every ‘npm install‘ command.
Yarn: yarn stores dependencies locally, and fetches from the disk during a ‘yarn add‘ command (assuming the dependency(with the specific version) is present locally).
Commands changed in yarn after npm

command: npm & yarn
Install dependencies: yarn
Install package_name npm install package_name
npm install package_name@version_number
yarn add package_name@version_number
Uninstall package:npm uninstall package_nameyarn remove package_name
Install dev package:npm install package_name –save-devyarn add package_name –dev
Update dev package:npm update package_name
npm update package_name@version_numberyarn upgrade package_name
yarn upgrade package_name@version_number
View package:npm view package_nameyarn info package_name
Global install package:npm install -g package_nameyarn global add package_name`

Personal Opinion:
Though my opinion doesn't matter because you may choose which one suits you still I wanted to share what I like.
I like yarn because It is lightweight fast and good for publishers as well.