logforth

Logforth

This is a simple logging framework specifically build for NodeJS.

I have been using several logging frameworks in the past, but I had always issues with one or another quirks of each. After comparing how each of them works, as well as looking for more inspiration in the Rust logging frameworks I came up with the design for this logging library.

Logforth supports both pretty printing for development and ndjson output for production. Each log entry has a mandatory message and optional attributes. Attributes are included as-is in ndjson output and pretty printed in development.

Installation

npm

npm i logforth

pnpm

pnpm add logforth

Usage

First you want to instantiate a new instance of the logger:

import {Logger} from "logforth";

const logger = new Logger();
logger.info("First logger test");

Min log level

By default, Logforth will log all events. You can limit this through the minLevel option:

import {Logger, LogLevel} from "logforth";

const logger = new Logger({ minLevel: LogLevel.Info });

In order to disable logging completely you can pass disableLogging to minLevel:

import {Logger, disableLogging} from "logforth";

const logger = new Logger({ minLevel: disableLogging });

Pretty printing

In development, you might prefer to see pretty printed log message. A simple switch between production and development could look like this:

import {Logger, NdJsonTransport, PrettyTransport} from "logforth";

const logger = new Logger({
    transport: process.env.NODE_ENV === "production"
        ? new NdJsonTransport()
        : new PrettyTransport()
});

Attributes

You can pass arbitrary attributes to each log entry:

logger.info("I contain attributes", { foo: "bar" });

In ndjson output they will be inlined with the rest of the log entry. Thus, you must not use the following attribute names: time, level and msg.

Default attributes

If you want to have specific attributes always present, e.g. the hostname of the running process, you can include this in the constructor:

const logger = new Logger({ attributes: { "hostname": "foo" } });

Context aware logging

Logforth supports logging in context aware situation, for instance when you want to keep track of a request ID. You can do so through the withContext() method. The following example demonstrates how to do this in Koa:

koaApp.use((context, next) => {
    return logger.withContext({ requestId: "foo" }, next);
});