function readSingleFile(evt) {
    //Retrieve the first (and only!) File from the FileList object
    var f = evt.target.files[0];

    if (!f) {
        alert("Failed to load file");
    } else if (!file.type.match('text.*')) {
		    alert(f.name + " is not a valid text file.);
    } else {
      var r = new FileReader();
      //proceed with read…
    }
  }