I was using the react-native package which I installed globally with npm. Now it says at the first line after executing the init command. The following:
Installing react-native from npm...
Consider installing yarn to make this faster: https://yarnpkg.com
So I was checking that website and it looked interesting to me, but I don't exactly know what it would be. At first, I thought that I would need brew to install yarn, so I could yarn to install npm. But now I think that yarn is a replacement of npm. Is that a correct statement?
Why would I like to have so many package managers?
I understand that it's useful for software like Atom or Visual Studio Code to have their own package manager. But for development, I do not see the reason why someone would like to use four different package managers (brew for 'primary software', yarn for npm packages, npm for backend modules and bower for front-end libraries). How can this package manager forest be untangled?
I am not familiar with brew, but I suppose you mean the Homebrew software package management system for macOS.
Then the purpose of each system is:
Yarn has some advantages over npm, the main two are the speed and the predictability. Yarn reuses the npm's package.json file and doesn't change its structure. Therefore you can run yarn install instead of npm install and theoretically everything will work automatically.
P.S. I agree, https://yarnpkg.com doesn't have enough background on why the hell we need another package management system, but there is a great article which fills that gap.