This package provides a lightweight structured logger that writes newline-delimited JSON to stdout by default. It supports syslog-style levels, named loggers, custom writable stream sinks, temporary log collection to an internal buffer, and Express HTTP logging middleware.

Getting started

npm install @saasquatch/logger

import { initializeLogger } from "@saasquatch/logger";

const logger = initializeLogger();
logger.info("Hello", { service: "example" });
logger.error(new Error("Something failed"));

const myValue = { field1: "string", field2: 1.2345 };
logger.debug({ message: "Trying to debug something here", myValue });

// child fields are included in every record emitted by the child
const requestLogger = logger.child({ requestId: "req-123" });
requestLogger.info("This log will include the above requestId field");

Customization of log sinks

import { createWriteStream } from "node:fs";
import { initializeLogger } from "@saasquatch/logger";

const logger = initializeLogger("my-logger", {
  level: "info",
  sinks: [
    // write to stdout (default)
    { stream: process.stdout },
    // write to stderr
    { stream: process.stderr },
    // write to log file
    { stream: createWriteStream("./service.log") },
  ],
});

Temporary log collection

import { initializeLogger } from "@saasquatch/logger";

const logger = initializeLogger();

// collect records for a response, while still writing them to the sink
logger.startLogCollection({ maxEntries: 100 });
logger.info("Request finished");

// logs: LogRecord[]
const logs = logger.getCollectedLogs();

// serializedLogs: string
const serializedLogs = logger.getCollectedLogs({ serialized: true });

logger.stopLogCollection();
logger.clearCollectedLogs();

Collection mode retains the newest 500 records by default. The size of the collection buffer can be customized by passing maxEntries to the startLogCollection function. Collection is independent for each logger and child logger.

The collected logs can be retrieved either in their raw or serialized form. Specifying { serialized: true } in the function options will use the logger's built-in serialization machinery on each collected log, then join the results with newlines.

Express HTTP logging

import express from "express";
import { httpLogMiddleware, initializeLogger } from "@saasquatch/logger";

const app = express();
const logger = initializeLogger();
app.use(httpLogMiddleware(logger));

HTTP records include the method, URL, status, response time, and request ID (if present). Common sensitive URL query parameters are removed by the middleware.