oops.js

const fs = require('fs')
const src = `/tmp/${Math.random()}`

Dat(src, (err, dat) => {
  if (err) throw err
  dat.archive.writeFile('/dat.json', 'hi', err => {
    if (err) throw err

    console.log(fs.readFileSync(`${src}/dat.json`)) // => empty
    dat.archive.readFile('/dat.json', (err, data) => {
      if (err) throw err // => error (couldn't satisfy length)
    })
  })
})