File logging library for Google Apps Script. You can create Log Document File in your script file folder and logging to the file.

In your Google Apps Script.

Menu > Resource > Library...

Enter ScriptId below.

1bWIXL3PmJQdgAjvUxY_qxStfTIdIMe7qwIqHq78XXzL3zyyVuhVvhI1S

Now you can use FileLogger class in your script.

In your function, you can just write your code like this.

function myFunction() {
  FileLogger.logging(function(){
    // your code here.
    Logger.log('test log');
  });
}

=> This will create a Document File name 'script.log' and write text below.

Sat Jan 20 01:21:07 JST 2018 INFO: test log

FileLogger.logging has a callback parameter. FileLogger create script.log Document File in a folder script file in if it doesn't exist. Every Logger.log in this callback are written to this log file after your code run.