gistfile1.js

function readAllHelps (cb) {
  var help_text = []
    , didError = false
  function error (er) {
    if (didError) return undefined
    didError = true
    cb(er)
  }
  fs.readdir('help', function(er, files) {
    if (err) return error(er)
    var len = files.length
    files.forEach(function (file) {
      fs.readFile('help/'+file, function(er, data) {
        if (didError) return undefined
        if(er) return error(er)
        help_text[file] = data
        if (0 === --len) cb(null, help_text)
      })
    })
  })
}

Thanks so much, you're a great help !

I think I now get how to structure my code thanks to your example.

I would never have come up with the counter decrementation to know when to call the callback... Very clever, I'll remember that trick.