loglevel-prefix

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

Installation

1npm install loglevel-prefix --save

API

1prefix(log[, options]);

log - root logger, imported from loglevel package

options - configuration object

1default_options = {
2  template: '[%t] %l:',
3  timestampFormatter: date => date.toTimeString().replace(/.*(\d{2}:\d{2}:\d{2}).*/, '$1'),
4  levelFormatter: level => level.toUpperCase(),
5  nameFormatter: name => name || 'root'
6}

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

1<script src="loglevel.min.js"></script>
2<script src="loglevel-prefix.min.js"></script>
3
4<script>
5  prefix(log);
6  log.warn('prefixed message');
7</script>

Output

[12:53:46] WARN: prefixed message

ES6

1
2import log from 'loglevel';
3import prefix from 'loglevel-prefix';
4
5prefix(log);
6log.warn('prefixed message');

CommonJS

1
2var log = require('loglevel');
3var prefix = require('loglevel-prefix');
4prefix(log);
5
6// or
7// var log = require('loglevel-prefix')(require('loglevel'));
8
9log.warn('prefixed message');

AMD

1define(['loglevel', 'loglevel-prefix'], function(log, prefix) {
2  prefix(log);
3  log.warn('prefixed message');
4});

Custom options

1import log from 'loglevel';
2import prefix from 'loglevel-prefix';
3
4prefix(log, {
5  template: '[%t] %l (%n) static text:',
6  timestampFormatter: date => date.toISOString(),
7  levelFormatter: level => level.charAt(0).toUpperCase() + level.substr(1),
8  nameFormatter: name => name || 'global'
9});
10
11log.warn('prefixed message');

Output

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

Example

1// moduleA.js
2import log from 'loglevel';
3
4export default function () {
5  log.warn('message from moduleA');
6}

1// moduleB.js
2import log from 'loglevel';
3
4const logger = log.getLogger('moduleB');
5
6export default function () {
7  logger.warn('message from moduleB');
8}

1// moduleC.js
2import log from 'loglevel';
3
4export default function () {
5  const logger = log.getLogger('moduleC');
6  logger.warn('message from moduleC');
7}

1// main.js
2import log from 'loglevel';
3import prefix from 'loglevel-prefix';
4
5import a from './moduleA';
6import b from './moduleB';
7import c from './moduleC';
8
9log.warn('message from root %s prefixing', 'before');
10
11prefix(log, {
12  template: '[%t] %l (%n):',
13});
14
15log.warn('message from root %s prefixing', 'after');
16
17a();
18b();
19c();

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

1// main.js
2import log from 'loglevel';
3import prefix from 'loglevel-prefix';
4
5log.setLevel('info');
6prefix(log);
7
8log.info('message from root after prefixing');
9
10try {
11  prefix(log, {
12    timestampFormatter: date => date.toISOString()
13  });
14} catch(e) {
15  log.error(e);
16};
17
18log.info('message from root after pre-prefixing');
19
20const logger = log.getLogger('main');
21
22try {
23  prefix(logger, {
24    template: '[%t] %l (%n):'
25  });
26} catch(e) {
27  logger.error(e);
28};
29
30logger.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