echo/README.md

@atums/echo

A minimal, flexible logger for Node with:

• Colored console output
• Daily .jsonl file logging
• Configurable output patterns
• Structured logs with caller metadata
• Fully typed config with environment/file/constructor override

---

Features

• Console and file logging with level-based filtering
• Colored output with ANSI formatting
• Daily rotated .jsonl files
• Supports runtime configuration merging
• Auto-formatted output using custom patterns
• Includes caller file, line, and column
• Pretty-prints structured objects if enabled
• Flushes open file streams on exit
• Uses Biome and EditorConfig for formatting and linting

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Installation

bun add @atums/echo

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Usage

import { echo } from "@atums/echo";

echo.info("App started");
echo.debug({ state: "init", ok: true });

try {
	throw new Error("Something failed");
} catch (err) {
	echo.error(err);
}

---

Configuration

Logger config can be defined in three ways:

1. JSON file (e.g. logger.json)
2. Environment variables
3. Constructor override

Priority (highest to lowest):

constructor > environment > logger.json > defaults

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logger.json example

{
  "directory": "logs",
  "level": "debug",
  "console": true,
  "consoleColor": true,
  "rotate": true,
  "maxFiles": 3,
  "prettyPrint": true,
  "pattern": "{color:gray}{timestamp}{reset} {color:levelColor}[{level-name}]{reset} ({file-name}:{line}:{column}) {data}",
  "customPattern": "{color:gray}{pretty-timestamp}{reset} {color:tagColor}[{tag}]{reset} {color:contextColor}({context}){reset} {data}",
  "customColors": {
    "GET": "green",
    "POST": "blue",
    "DELETE": "red"
  }
}

---

Supported Environment Variables

Variable	Description
LOG_LEVEL	Log level (debug, info, etc.)
LOG_LEVEL_COLOR	Comma-separated list of TAG:color pairs
LOG_DIRECTORY	Log directory path (default: logs)
LOG_DISABLE_FILE	Disable file output (true or false)
LOG_ROTATE	Enable daily rotation
LOG_MAX_FILES	Max rotated files to keep
LOG_CONSOLE	Enable console output
LOG_CONSOLE_COLOR	Enable ANSI color in console output
LOG_DATE_FORMAT	Date format for display timestamp
LOG_TIMEZONE	Timezone (local or IANA string)
LOG_SILENT	Completely disable output
LOG_PATTERN	Custom log format for console
LOG_PRETTY_PRINT	Pretty-print objects in console output
LOG_CUSTOM_PATTERN	Pattern used for echo.custom() logs
LOG_CUSTOM_COLORS	Comma-separated list of TAG:color pairs

---

Pattern Tokens

These tokens are replaced in the log pattern:

Token	Description
{timestamp}	ISO timestamp string
{pretty-timestamp}	Formatted display timestamp
{level-name}	Uppercase log level (e.g. DEBUG)
{level}	Numeric log level
{file-name}	Source filename
{line}	Line number in source
{column}	Column number in source
{data}	Formatted log data (message/object)
{id}	Unique short ID for the log
{tag}	Custom tag used in echo.custom()
{context}	Custom context in echo.custom()
{color:*}	ANSI color start (e.g. {color:red})
{color:levelColor}	Dynamic color based on log level
{color:tagColor}	Color for custom tag
{color:contextColor}	Color for custom context
{reset}	Resets console color

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Custom Log Entries

You can log arbitrary tagged messages with echo.custom(tag, context, message):

echo.custom("GET", "/health", { status: 200 });

The output format is controlled by:

• customPattern — e.g. {pretty-timestamp} [GET] (/health) { status: 200 }
• customColors — define colors for tags like "GET": "green"

Example output

2025-05-24 16:22:00.123 [GET] (/health) { status: 200 }

---

Output Examples

Console (with colors)

2025-05-24 16:15:00.000 [INFO] (index.ts:3:6) Server started

File (logs/2025-05-24.jsonl)

Each line is structured JSON:

{
  "timestamp": 1748115300000,
  "level": "info",
  "id": "aB4cD9xZ",
  "file": "index.ts",
  "line": "3",
  "column": "6",
  "data": "Server started"
}

If an error is logged:

{
  "timestamp": 1748115301000,
  "level": "error",
  "id": "qW3eR7tU",
  "file": "index.ts",
  "line": "10",
  "column": "12",
  "data": {
    "name": "Error",
    "message": "Something failed",
    "stack": "Error: Something failed\n  at index.ts:10:12"
  }
}

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Development

This project uses:

• TypeScript
• Bun runtime
• Biome for formatting/linting
• JSONL for structured file output
• date-fns-tz for timezone support

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Images

Logger preview (pretty)

Logger preview (no pretty)

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License

BSD 3-Clause License