inside a worker (which would basically be the equivalent of self.console.log('test');, as these are being called on the worker scope, which can be referenced with WorkerGlobalScope.self), to return a test message out to the browser console.
If you are calling console.log() from a DedicatedWorkerGlobalScope or other worker scope that acts on a single loaded window, that tab's web console will receive the logs. However, If you are calling console.log() from a SharedWorkerGlobalScope, the global browser console will receive the logs.
補足 Before Firefox 30, the console would be of type WorkerConsole instead of Console.