How do I view the size of npm packages?

What you probably want to measure is the impact a package has if you were to add it to your app bundle. Most of the other answers will estimate the size of the source files only, which maybe inaccurate due to inline comments, long var names etc.

There is a small utility I made that'll tell you the min + gzipped size of the package after it gets into you bundle -

https://bundlephobia.com

Take a look at this cost-of-modules project. It's an npm package that will list the size of a package and number of children.

Installation: npm install -g cost-of-modules

Usage: Run cost-of-modules in the directory you are working in.