Yadah Logger subsystem

A Yadah subsystem and Domain class mixin that provides a logging using winston.

Basic usage

import createLogger, { LoggerMixin } from "@yadah/subsystem-logger";
import DataManager, { Domain } from "@yadah/data-manager";
import { pipe } from "@yadah/mixin";

class MyDomain extends pipe(Domain, LoggerMixin) {
  foo() {
    this.logger.info("foo() was called");
  }

  err() {
    try {
      throw new Error("error message");
    } catch (error) {
      this.logger.error("err() threw", error);
    }
  }
}

const logger = createLogger({ pretty: true, silent: false, level: "info" });

const dataManager = new DataManager({ logger });
const domains = dataManager.boot({ MyDomain });

domains.MyDomain.foo();
// info: foo() was called {timestamp}

domains.MyDomain.err();
// error: err() threw {timestamp}
// Error: error message
//   {stack}

Logging types

The logger instance provides access to syslog, npm, and cli logging types.

logger.syslog.warning("A syslog style warning");
logger.cli.help("A help message");
logger.npm.http("request", request);

The options.level option may be set to a comma-separated list of levels. Each logging type will use the first level that the logger supports. For example, to output only syslog "alert" and above messages and otherwise "error" messages, set { level: "alert,error" }. To get all levels for each type use { level: "silly,debug" }.

Log formats

The logger has two formats:

• pretty
• json

In each format, the log functions accept arguments in the form:

logger.info(message: string, ...metaData: any[]);

Note: No string interpolation is performed.

The "pretty" format is intended for development environments. It will display the message and each metaData item as colorized output. Error objects are displayed with a stack trace.

The "json" format is intended for production environments where logs are captured in a centralized logging tool. Error objects are captured with a stack trace.

createLogger(options)

Creates a winston logger configured to output logs to the console.

Options:

• pretty - set to true in development to output readable logs; set to false in production to output JSON content more suitable for machine consumption
• silent - set to true to suppress all log output
• level - only log messages at or above this level will be output; set to "silly,debug" to get maximum logs; default is "info"

LoggerMixin

The LoggerMixin function will add a .logger property to domain classes which provides access to the logger instance.