gistfile1.js

// Folder.js has folders object and files object
// Here we need to load a Folder's files and update some permission, until there is no folder anymore


 function shareFolderRecursively(id, permission,cb){
            Folder
                .findOne({ id: id })
                .populate('files')
                .populate('folders')
                .exec(function(err,folder){
                    if(err){
                        console.log(err);
                    }
                    /** Loop trough all the current folder's files and update their permissions **/
                    async.each(
                        folder.files,
                        function shareFile(file,callback){
                            file.permission = permission;
                            file.save(function(err){
                                if(err){
                                    callback(err);
                                }
                                else{
                                    callback();
                                }
                            });
                        },
                        function(err){
                            if(err){
                                console.log(err);
                            }
                            else if(folder.folders.length > 0 ){
                                async.each(
                                    folder.folders,
                                    function reLoop(folder,callback2){
                                        shareFolderRecursively(folder.id,permission,callback2);
                                    },
                                    function(err){
                                        if(err){
                                            console.log(err);
                                        }
                                        console.log('EVERYTHING IS DONE ');
                                    }
                                );
                            }
                            else{
                                cb();
                            }
                        }
                    );
                });
        }