...var downloadedFile = sftp.download({...}); downloadedFile.folder =1234; downloadedFile.save();...

require(['N/sftp','N/file'],function(sftp, file){var connection = sftp.createConnection({/* The Username supplied by the administrator of the external SFTP server. */ username:'myuser',/* Refers to the Password supplied by the administrator of the external SFTP server. The Password Token/GUID obtained by reading the form POST parameter associated with user submission of a form containing a Credential Field. Value would typically be read from a custom field. */ passwordGUID:"B34672495064525E5D65032D63B52301",/* The URL supplied by the administrator of the external SFTP server. */ url:'host.somewhere.com',/* The SFTP Port number supplied by the administrator of the external SFTP server (defaults to 22). */ port:22,/* The transfer directory supplied by the administrator of the external SFTP server (optional). */ directory:'transferfiles',/* RSA Host Key obtained using the ssh-keyscan tool. $ ssh-keyscan -t rsa -p 22 host.somewhere.com AATpn1P9jB+cQx9Jq9UeZjA1245X7SBDcRiKh+Sok56VzSw== */ hostKey:"AATpn1P9jB+cQx9Jq9UeZjA1245X7SBDcRiKh+Sok56VzSw=="});/* Creating a simple file. */var myFileToUpload = file.create({ name:'originalname.js', fileType: file.Type.PLAINTEXT, contents:'I am a test file. Hear me roar.'});/* Uploading the file to the external SFTP server. */ connection.upload({/* Subdirectory within the transfer directory specified when connecting (optional). */ directory:'relative/path/to/remote/dir',/* Alternate file name to use instead of the one given to the file object (optional). */ filename:'newFileNameOnServer.js',/* The file to upload. */ file: myFileToUpload,/* If a file already exists with that name, replace it instead of failing the upload. */ replaceExisting:true});var downloadedFile = connection.download({/* Subdirectory within the transfer directory specified when connecting (optional). */ directory:'relative/path/to/file',/* The name of the file within the above directory on the external SFTP server which to download. */ filename:'downloadMe.js'});});