JSON logging configuration for JavaScript using log4js (python compatible)

logger.js

/**
 * This configuration uses log4js and outputs logs to stdout
 * in JSON format. The names of the fields are compatible with
 * python-json-logger.
 *
 * The configuration was developed to the purposes of logging
 * Express JS logs running inside docker and collected through
 * FluentD.
 *
 * Reported fields:
 *   name: my.logger
 *   level: INFO
 *   message: ekrjgnwle
 *   timestamp: %Y-%m-%dT%H:%M:%S.%N%z
 */

const log4js = require("log4js");

log4js.configure({
  appenders: {
    stdout: {
      type: "stdout",
      layout: {
        type: "pattern",
        //pattern: `{"timestamp": "%d{yyyy-MM-ddThh:mm:ss.SSSO}", "name": "%c", "level": "%p", "message": "%m{0}"}`,
        pattern: `{"timestamp": "%d{ISO8601_WITH_TZ_OFFSET}", "name": "%c", "level": "%p", "message": "%m{0}"}`,
      },
    },
  },
  categories: {
    default: { appenders: ["stdout"], level: "info" },
  },
});

exports.logger = log4js.getLogger("server");