GASスニペット

function myFunction() {
    getFileWhile();
     var root = DriveApp.getRootFolder()
     var key = root.getId();
     Logger.log('key=' + key);
}

function getFileWhile() {
    var files = DriveApp.getFolderById('').getFiles();
    Logger.log('hello1');
    while(files.hasNext()) {
        var file = files.next();
        var filename = file.getName()
        Logger.log(filename);
    }
    Logger.log('hello2');
}

var file_name = 'file.txt';
var folder_name = 'dir1';
var folderID = DriveApp.getFoldersByName(folder_name).next().getId();
var fileIT = DriveApp.getFolderById(folderID).getFilesByName(file_name).next();
var textdata = fileIT.getBlob().getDataAsString('utf8');
Logger.log(textdata);