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Isomorphic Logger

Note: This package is a (hard)-fork of @grabrinc//isomorphic-logger which suddenly disappeared from the face of the internet. This fork attempts to rewrite, mordernize, and bring new features.

Tiny isomorphic logger that has the same semantics on the server and on the client with multi-channel support and modular structure.

import { Logger, createConsoleProcessor } from "@isplasher/isomorphic-logger";

const logger = new Logger();

logger.channel(createConsoleProcessor());

logger.log("Hello world!", { foo: "bar" }); // → Prints "Hello world! {foo: 'bar'}" to console

Logging

These methods are available on Logger instance and log messages at corresponding log level:

  • trace(...messages)
  • debug(...messages)
  • info(...messages) there's a convinient alias log(...messages)
  • warn(...messages)
  • error(...messages)

Each method accepts an arbitrary number of arguments as console.log does.

Logging Level

Setting log level on Logger instance allows to limit verbosity of the output:

import { LogLevel } from "@isplasher/isomorphic-logger";

// Now messages with warn level or higher are logged.
logger.setLevel(LogLevel.WARN);

Following log levels are available out-of-the-box:

  • LogLevel.TRACE
  • LogLevel.DEBUG
  • LogLevel.INFO
  • LogLevel.WARN
  • LogLevel.ERROR
  • LogLevel.OFF no messages would be logged with this level.

You can create your own log level via instantinating LogLevel class:

logger.setLevel(new LogLevel(150));

Logging Level Test

If you want to perform heavy computations when particular logging level is set, you can use logging level test methods:

if (logger.isDebugEnabled()) {
  // Do heavy stuff here
  logger.debug("Computation results");
}

These methods are availeble on Logger instance:

  • isTraceEnabled()
  • isDebugEnabled()
  • isInfoEnabled()
  • isWarnEnabled()
  • isErrorEnabled()

Channels

To set up a logger instance you need to define at least one channel.

Channel consists of processors that are executed one after another and can be asynchronous.

import {
  Logger,
  createStackTraceTransformProcessor,
  createDateAndLevelPrependProcessor,
  createThrottleProcessor,
  createConsoleProcessor,
} from "@isplasher/isomorphic-logger";
import * as Sentry from "@sentry/node"; // or @sentry/<platform>

logger.channel(
  createStackTraceTransformProcessor(), // Converts error objects to string representing stack trace.
  createDateAndLevelPrependProcessor(), // Prepends every message with date and time.
  createThrottleProcessor({ delay: 500, length: 10 }), // Batch logged messages.
  createConsoleProcessor() // Write batched messages to console.
);

logger.channel(
  createMessageConcatProcessor(), // Concat all messages into a single string.
  createErrorWrapProcessor(), // Wrap message into an Error object and trim excessive stack frames.
  createSentryProcessor(Sentry) // Send messages to Sentry.
);

logger.log("Hello there!"); // This is logged to both console and Sentry

Even if the channel contains an asynchronous processor, messages are guaranteed to be logged in the original order.

Logger itself is also a processor, so you can nest one logger into another:

const errorLogger = new Logger();
errorLogger.setLevel(LogLevel.ERROR);
errorLogger.channel(createSentryProcessor(Sentry));

const logger = new Logger();
logger.setLevel(LogLevel.TRACE);
logger.channel(createConsoleProcessor());
logger.channel(errorLogger);

logger.log("Foo"); // This is logged in the console only

logger.error("Oh snap!"); // This is logged in the console and send to Sentry

Available Processors

Following processors are available at the moment:

There are also server-only processors available which can be imported from @isplasher/isomorphic-logger/server:

How to create a custom processor?

A processor is a function that receives a set of records:

type Record = {
  level: LogLevel;
  messages: any[];
};

function myCustomProcessor(
  records: Record[]
): Promise<Record[]> | Record[] | Promise<null> | null {
  return records;
}

Or an object that has process function property:

const myCustomProcessor = {
  process(
    records: Record[]
  ): Promise<Record[]> | Record[] | Promise<null> | null {
    return records;
  },
};

A processor should do some stuff with messages and return a new set of records that is passed to the next processor.

If processor returns false value than next processor is not invoked.

A processor can return Promise that is awaited before proceeding to next processor.

If you need to ensure logging was completed before continuing code execution you can await the log call:

await logger.error("Wait for this messages to log!", error);

Declarative Logger Configuration

Logger can be created from JSON configuration:

import {parseLoggerConfig, ProcessorFactories} from '@isplasher/isomorphic-logger';

const loggerConfig = {
  level: 'TRACE',
  channels: [
    [
      {type: 'throttle', options: {delay: 1000, length: 10}}
      {type: 'extractStackTrace'},
      {type: 'highlight'},
      {type: 'console'}
    ],
    [
      {
        type: 'logger',
        options: {
          level: 'ERROR',
          channels: [
            [
              {type: 'prependDateAndLevel'},
              {type: 'console'}
            ]
          ]
        }
      }
    ]
  ]
};

const logger = parseLoggerConfig(loggerConfig, ProcessorFactories);

License

The code is available under MIT license.