Logging¶

Creating a logger¶

const logger = new Logger();

You can also give the logger a name to help discern it in the output:

const logger = new Logger('Example');

You can create a filtered logger, which will only emit at or above the given log level:

const logger = new Logger('Example', LogLevel.Information);

You can create child loggers which forward output to the same transports:

const child = logger.createChild();
const child = logger.createChild('Child');
const child = logger.createChild('Child', LogLevel.Information);

Attaching transports¶

Using the `create` methods¶

There are methods on the Logger class to easily create and attach one of the built-in transports. For custom transports, you'll need to use the attach method as documented further below.

logger.createConsoleTransport();

logger.createFileTransport({
    fileName: 'console.log'
});

Check the transports documentation to see the available options for these methods.

Using the `attach` method¶

When working with custom transports, or when you want to attach multiple root loggers to a single transport, you'll need to instantiate the transport manually and then attach the logger(s).

const transport = new ConsoleTransport({ /* options */ });
transport.attach(logger);

Getting attached transports¶

The transports field on a logger will return an array of all attached transports, including those attached to parent logger(s). This is most useful for gracefully closing all attached transports:

await Promise.all(
    logger.transports.map(transport => transport.close())
);

Logging levels¶

Name	Value	Description
`Trace`	`0`	Logs that contain the most detailed messages. These messages can contain sensitive application data. These messages should not be used in a production environment.
`Debug`	`1`	Logs that are used for interactive investigation during development. These logs should primarily contain information useful for debugging and have no long-term value.
`Information`	`2`	Logs that track the general flow of the application. These logs should have long-term value.
`Warning`	`3`	Logs that highlight an abnormal or unexpected event in the application flow, but do not otherwise cause the application execution to stop.
`Error`	`4`	Logs that highlight when the current flow of execution is stopped due to a failure. These should indicate a failure in the current activity, not an application-wide failure.
`Critical`	`5`	Logs that describe an unrecoverable application or system crash, or a catastrophic failure that requires immediate attention.
`None`	`6`	Not used for writing log messages. Specifies that a logging category should not write any messages.

Events¶

`output`¶

This event is emitted when the logger receives new output from the application.

Argument	Types	Description
`output`	`LoggerOutput`	An object containing details about the output message.