Can I install NPM and YARN alternately?
If I need package a and package b, can I install package a with NPM and package b with YARN?
npm install a
yarn add b
Yarn is fine alone, and I don't see personnally why you need use both for a project. But yes, you can install both in the same project.
In case you would like to see the advantages of Yarn over Npm, I'll slip you this little link: https://www.sitepoint.com/yarn-vs-npm/