loglevel-prefix

loglevel-prefix

Minimal, dependency-free and lightweight (0.9KB minified and gzipped) plugin for loglevel message prefixing

Installation

npm install loglevel-prefix --save

API

prefix(loglevel[, options]);

loglevel - root logger object, imported from loglevel package

options - configuration object

Base usage

Browser directly

Download production version and copy to your project folder

<script src="loglevel.min.js"></script>
<script src="loglevel-prefix.min.js"></script>

<script>
  prefix(log);
  log.warn('prefixed message');
</script>

ES6

import log from 'loglevel';
import prefix from 'loglevel-prefix';

prefix(log);
log.warn('prefixed message');

CommonJS

var log = require('loglevel');
var prefix = require('loglevel-prefix');
prefix(log);

// or
// var log = require('loglevel-prefix')(require('loglevel'));

log.warn('prefixed message');

AMD

define(['loglevel', 'loglevel-prefix'], function(log, prefix) {
  prefix(log);
  log.warn('prefixed message');
});

Options

Default options

options = {
  format: '[%t] %l:',
  dateFormatter: date => date.toTimeString().replace(/.*(\d{2}:\d{2}:\d{2}).*/, '$1'),
  levelFormatter: level => level.toUpperCase(),
  nameFormatter: name => name || 'root'
}

Output

[12:53:46] WARN: prefixed message

Custom options

import log from 'loglevel';
import prefix from 'loglevel-prefix';

prefix(log, {
  format: '[%t] %l (%n) <static>:',
  dateFormatter: date => date.toISOString(),
  levelFormatter: level => level.charAt(0).toUpperCase() + level.substr(1),
  nameFormatter: name => name || 'global'
});

log.warn('prefixed message');

Output

[2017-05-29T16:53:46.000Z] Warn (global) <static>: prefixed message

Usage

// moduleA.js
import log from 'loglevel';

export default function () {
  log.warn('message from moduleA');
}

// moduleB.js
import loglevel from 'loglevel';
const log = loglevel.getLogger('moduleB');

export default function () {
  log.warn('message from moduleB');
}

// moduleC.js
import loglevel from 'loglevel';

export default function () {
  const log = loglevel.getLogger('moduleC');
  log.warn('message from moduleC');
}

// main.js
import log from 'loglevel';
import prefix from 'loglevel-prefix';

import a from './moduleA';
import b from './moduleB';
import c from './moduleC';

log.warn('message from root before prefixing');

prefix(log, {
  format: '[%t] %l (%n):',
});

log.warn('message from root after prefixing');

a();
b();
c();

prefix(log, {
  format: '[%t] %l (%n):',
  dateFormatter: date => date.toISOString()
});

log.warn('message from root after pre-prefixing');

Output

message from root before prefixing
[16:53:46] WARN (root): message from root after prefixing
[16:53:46] WARN (root): message from moduleA
message from moduleB
[16:53:46] WARN (moduleC): message from moduleC
Uncaught TypeError: You can assign a prefix only one time

Note

// main.js
import loglevel from 'loglevel';
import prefix from 'loglevel-prefix';

loglevel.warn('message from root');

const log = loglevel.getLogger('main');

prefix(log, {
  format: '[%t] %l (%n):',
  dateFormatter: date => date.toISOString()
});

log.warn('message from main');

Output

message from root
Uncaught TypeError: Argument is not a root loglevel object