loglevel-prefix

loglevel-prefix

Minimal lightweight (0.9KB minified and gzipped) plugin for loglevel message prefixing

Installation

npm install loglevel-prefix --save

API

prefix(log[, options]);

log - root logger, imported from loglevel package

options - configuration object

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

Plugin formats the prefix using template option as a printf-like format.

The template is a string containing zero or more placeholder tokens. Each placeholder token is replaced with the value from loglevel messages parameters. Supported placeholders are:

%t - Timestamp of message.

%l - Level of message.

%n - Name of logger.

The timestampFormatter, levelFormatter and nameFormatter is a functions for formatting corresponding values

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>

Output

[12:53:46] WARN: prefixed message

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');
});

Custom options

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

prefix(log, {
  template: '[%t] %l (%n) static text:',
  timestampFormatter: 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 text: prefixed message

Example

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

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

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

const logger = log.getLogger('moduleB');

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

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

export default function () {
  const logger = log.getLogger('moduleC');
  logger.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 %s prefixing', 'before');

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

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

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

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

Errors

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

log.setLevel('info');
prefix(log);

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

try {
  prefix(log, {
    timestampFormatter: date => date.toISOString()
  });
} catch(e) {
  log.error(e);
};

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

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

try {
  prefix(logger, {
    template: '[%t] %l (%n):'
  });
} catch(e) {
  logger.error(e);
};

logger.info('message from child logger');

Output

[16:53:46] INFO: message from root after prefixing
[16:53:46] ERROR: TypeError: You can assign a prefix only one time
[16:53:46] INFO: message from root after pre-prefixing
[16:53:46] ERROR: TypeError: Argument is not a root loglevel object
[16:53:46] INFO: message from child logger