multiple async filereader onloads

mafo.js

for (var i in files) {
   var file = files[i];
   var reader = new FileReader();
   reader.onload = (function(detail) {
     return function(e) {
       var plaintext = e.target.result;
       console.log(plaintext);
     };
   })(file);
   reader.readAsText(file);
}