title: Read files in series with fs.readFile in Node?
body: <p>I have an arbitrary number file paths stored in an array as strings.</p>
  
  <p>I need to read these files in series (i.e. finish reading one file before starting reading the next one), and output the file length after each file read. And after finish reading all files, print <code>'done'</code>.</p>
  
  <p>I'm only allowed to use <code>fs.readFile</code> and native Javascript. No <code>fs.readFileSync</code> or any other module is allowed. Also, I'm on Node v6, so I can't use async/await.</p>
  
  <p>Is there any way to implement the functionality, following the constraints?</p>