@nayotta/mta-logger

A simple typescript/javascript logger module.

install

$ npm install @nayotta/mta-logger --save

use

log levels: trace, debug, info, warn, error, fatal, panic, off.

inside formats

import { Logger, formats } from "@nayotta/mta-logger";

const logger = new Logger({
  level: "debug",
  format: formats.default, // default
  // format: formats.json,
  // format: formats.text,
}).withFields({
  "#instance": "app",
  "#method": "init",
});

logger.info("app start on port", 8080);

// default print
// INFO[2021-10-13T15:20:19:042] app start on port 8080 #instance=app #method=init

// json print
// {"level":"info","time":"2023-07-10 15:18:38.7","#instance":"app","#method":"init","msg":"app start on port 8080"}

// text print
// level=info time="2023-07-10 15:22:44.513" msg="app start on port 8080" #instance=app #method=init

logger.infof("app start on port %s", 8080);

// default print
// INFO[2021-10-13T15:20:19:042] app start on port 8080           #instance=app #method=init

// json print
// {"level":"info","time":"2023-07-10 15:18:38.7","#instance":"app","#method":"init","msg":"app start on port 8080"}

// text print
// level=info time="2023-07-10 15:22:44.513" msg="app start on port 8080" #instance=app #method=init

// rich format specifiers (powered by sprintf-js)
logger.infof("user %s has %d messages, %.1f%% done", "Alice", 5, 87.6);
// → user Alice has 5 messages, 87.6% done

logger.debugf("hex: 0x%04X, oct: %o, bin: %b", 255, 8, 5);
// → hex: 0x00FF, oct: 10, bin: 101

logger.errorf("[%10s] %-10s | count=%04d", "worker", "ok", 42);
// → [    worker] ok         | count=0042

supported format specifiers

Powered by sprintf-js, the *f methods support full C/printf-style formatting:

| specifier | description | example | | ----------- | --------------------------- | ------------------------ | | %s | string (default) | %s → hello | | %d / %i | signed decimal integer | %d → 42 | | %f | floating point | %f → 3.14 | | %.Nf | float with N decimal places | %.2f → 3.14 | | %x / %X | hex (lower/upper) | %x → ff, %X → FF | | %o | octal | %o → 10 | | %b | binary | %b → 101 | | %e | scientific notation | %e → 1.000000e+2 | | %t | boolean | %t → true | | %% | literal percent | %% → % |

Width, alignment and padding:

| flag | description | example | output | | ------ | ---------------------------- | --------------- | ------------ | | %Ns | right-align, width N | %10s, 'hi' | hi | | %-Ns | left-align, width N | %-10s, 'hi' | hi | | %0Nd | zero-padded integer, width N | %04d, 7 | 0007 |

colorful option

The colorful option adds color to log level prefixes and field keys to improve readability. It works in both terminal and browser environments with different underlying mechanisms:

| environment | mechanism | example | | ------------------ | ----------------- | ------------------------------------------- | | terminal (Node.js) | ANSI escape codes | \x1b[36mDEBU\x1b[0m → colored text | | browser (DevTools) | %c CSS styles | %cDEBU%c + color: #56b6c2 → styled text |

const logger = new Logger({
  level: "debug",
  colorful: true, // default: false
});

logger.info("server started");
// terminal: \x1b[36mINFO\x1b[0m[2026-...] server started
// browser: %cINFO%c[2026-...] server started

logger.debugf("request %s processed in %dms", "GET /api", 42);

When colorful is enabled, the output array includes CSS style parameters for browser console.log's %c substitution — no extra configuration needed.

custom format

Also, you can make a custom format function to build your own log format.

import { Logger, TLogItem formats } from '@nayotta/mta-logger'

const logger = new Logger({
	level: 'debug',
	format: function (logItem: TLogItem) {
		const out: any[] = []
		const { level, time, error, logs, fields, colorful } = logItem
		// TODO: build your own custom log format
		// like:
		out.push(`${level.toUpperCase()}`)
		out.push(`t="${time.toLocaleString()}"`)
		for (const log of logs) {
			out.push(log)
		}
		if (error) {
			out.push(`err=${error.message}`)
		}
		for (const key in fields) {
			out.push(`${key}=${fields[key]}`)
		}
		// console.log(...out)
		return out
	}
}).withFields({
	'#instance': 'app',
	'#method': 'init'
})

logger.info('app start on port', 8080)

// print
// INFO t="7/10/2023, 3:31:01 PM" app start on port 8080 #instance=app #method=init

logger.infof('app start on port %s', 8080)

// print
// INFO t="7/10/2023, 3:31:01 PM" app start on port 8080           #instance=app #method=init

log hooks

With log hooks, you can catch log action happened.

import { Logger, TLogItem formats } from '@nayotta/mta-logger'

const logger = new Logger({
	level: 'debug'
}).addLogHooks([{
	levels: ['error', 'fatal', 'panic'],
	callback: async function (logItem: TLogItem) {
		// TODO: do something
		console.log('send error message with log item:', logItem)
	}
}])

logger.withError(new Error('test')).error('failed to do something')