Logger

The Logger module provides structured, leveled logging with support for JSON and human-readable output formats.

Usage

import { FluxKit } from "@fluxkitdev/core";

const app = new FluxKit({
  database: { uri: process.env.MONGODB_URI },
  logger: {
    level: "debug",
    format: "pretty", // "json" for production
  },
});

app.logger.debug("Debugging info", { userId: "123" });
app.logger.info("User logged in", { userId: "123", ip: "1.2.3.4" });
app.logger.warn("Rate limit approaching", { current: 95, max: 100 });
app.logger.error("Failed to send email", { error: err.message });

API Reference

logger.debug(message: string, meta?: object): void

Log a debug-level message. Only visible when LOG_LEVEL is set to debug.

logger.info(message: string, meta?: object): void

Log an informational message.

logger.warn(message: string, meta?: object): void

Log a warning message.

logger.error(message: string, meta?: object): void

Log an error message.

logger.child(meta: object): Logger

Create a child logger that inherits the parent's configuration and merges additional metadata into every log entry.

const reqLogger = app.logger.child({
  requestId: "abc-123",
  path: "/api/users",
});

reqLogger.info("Processing request");
// Output includes requestId and path automatically

Log Levels

Level	Priority	Description
debug	0	Detailed debugging information
info	1	General operational messages
warn	2	Warning conditions
error	3	Error conditions

Setting LOG_LEVEL=warn will suppress debug and info messages.

Output Formats

Pretty (Development)

[2025-01-15 10:30:45] INFO  User logged in  userId=123 ip=1.2.3.4

JSON (Production)

{
  "timestamp": "2025-01-15T10:30:45.123Z",
  "level": "info",
  "message": "User logged in",
  "userId": "123",
  "ip": "1.2.3.4"
}

Configuration

Variable	Default	Description
LOG_LEVEL	info	Minimum log level
LOG_FORMAT	json	Output format (json or pretty)