title: How npmjs.com calculates the code quality
body: <p>When we publish a package to npm, it will show us some data such as popularity, quality, and maintenance in the search page (The example image is blow). 
  I just wonder how npm calculates the quality? Really appreciate if someone can give some clue. </p>
  
  <p><a href="https://i.stack.imgur.com/av8Oq.png" rel="noreferrer"><img src="https://i.stack.imgur.com/av8Oq.png" alt="enter image description here"></a></p>
  
  <p>You can see this if you look on the search page.  See the right side of search page: <a href="https://www.npmjs.com/search?q=react" rel="noreferrer">npm search for "react"</a></p>