Simple and flexible logger for the browser and Node.js


Another loggging library!? Yes. But this one is different. It's written with both the client and server in mind. It has the same API when runnning on the client or server (Node.js), supports being required in Node/Browserified apps, and also can be installed using Bower; great news if you want to use the same log library on both the client and server! It's also possible to use with AngularJS' dependency injection.

var Logger = require('fhlog'); // May also use window.fhlog 
    meta: {
        deviceId: '123321123321'
}, function (err) {
    if (err) {
        // Custom logic to handle it 
    // Create a logger for "Stats" component and set the level to DEBUG 
    var stats = Logger.getLogger('Stats', {
        level: Logger.LEVELS.DBG,
        // upload: true/false - Should these be uploaded? 
        // silent: true/false - Silence all output from this logger? 
    // Log levels 
    stats.debug('I\'ll log at DEBUG level!');
    stats.info('I\'ll log at INFO level!');
    stats.warn('I\'ll log at WARN level!');
    stats.error('I\'ll log at ERROR level!');
    // Setting a logger level 
    stats.d('I won\'t be written to console/stdout. My level is too low.');
    stats.i('I won\'t be written to console/stdout either!');
    stats.w('I\'ll log at WARN level!');
    stats.e('I\'ll log at ERROR level!');
    // Getters / Setters 
    stats.getName() // returns 'Stats' 
    stats.setName('New Name!') // You probably won't need to use this really 
    var curLvl = stats.getLogLevel();
    stats.info('My log level is %d', curLvl);

If we run the above example the following output is generated.

2014-10-01T17:27:57.188Z DBG Stats: I'll log at DEBUG level!
2014-10-01T17:27:57.197Z INF Stats: I'll log at INFO level!
2014-10-01T17:27:57.197Z WRN Stats: I'll log at WARN level!
2014-10-01T17:27:57.197Z ERR Stats: I'll log at ERROR level!
2014-10-01T17:27:57.198Z WRN Stats: I'll log at WARN level!
2014-10-01T17:27:57.198Z ERR Stats: I'll log at ERROR level!
2014-10-01T17:27:57.198Z INF New Name!: My log level is 0

Works just like it usually does, but can be injected as a service instance into other components. Just add it as a dependency of your module.

angular.module('MyApp', ['fhlog']);
angular.module('MyApp').service('Heroes', function (fhlog) {
    var log = fhlog.getLogger('Heroes Service');
    var heroes = ['Batman', 'Spiderman', 'Thor'];
    this.get = function () {
        log.d('Getting heroes!');
        return heroes;

This feature is not thoroughly tested yet, so be mindful of that. Currently it will only work on Chrome, Opera and Cordova applications that support the FileSystem API.

Logs can easily be uploaded to a server. Just call the init method on the Logger and set an uploadFn. This function must accept a string parameter and a callback you need to call once the upload process completes or fails. The callback function takes a single parameter, an error, if one occured. An example is below.

function myUploadFn (jsonLogArraycallback) {
    // Do your upload logic... 
    if (uploadError) {
    } else {
// Initialise the logger with an upload function 
    uploadFn: myUploadFn
// Anything logged using this logger will be uploaded 
// if its logged using INF or higher, they'll also be written 
// to the terminal/console 
Logger.getLogger('Stats', {
    level: Logger.LEVELS.INF
    upload: true,
    silent: false

This is the primary interface exposed when you require this module, or on the window.fhlog object if you're not using Browserify or Node.js.

Set a default value to use for a paramter when getting a logger. For example you might want all loggers to not use colours so you could do this.

var fhlog = require('fhlog');
fhlog.setDefault('colourise', false);

Exposes a way to set log levels. Contains the following keys for use as shown in previous examples.

  • DBG
  • INF
  • WRN
  • ERR

An interface to set/get/remove/replace data in the metadata included with each log upload. Check out the Meta section below for more info/

Initialise the LoggerFactory (fhlog). You don't need to call this at present but it is highly recomended that you do. The options object passed can contain:

  • meta - Extra data to upload with each log, e.g a uqique device ID or username. This must be an object.
  • uploadFn - A function that will handle uploading the JSON string of logs.
  • storageQuota - The amount of bytes allocated to store log data. This will gradually fill up as you use Logger instances that have the upload flag set to true but will also decrease as these logs are uploaded.
var Logger = require('fhlog');
    uploadFn: myUploadFn,
    meta: {
        deviceId: '123321123321'
    stroageQuota: 50 * Math.pow(1024, 3) // 50MB of logs can be stored 

Set all loggers to the provided level.

Get a logger prefixed with the given name. Valid options for the opts are:

  • level - Defaults to LEVELS.DBG.
  • upload - Defaults to false.
  • silent - Defaults to false.
  • colourise - Defaults to true. Colours don't work in the browser so this is ignored.

Meta stores data that will be included with each log message that's uploaded. For example a device ID or the username that is current logged in. It shouldn't be used to hold large payloads and should be strictly minimal metadata.

Meta is a JSON object so it contains key pair data. All added data must be valid serialisable JSON as it will be stringified for upload.

Get the value stored in metadata for key;

Store the value val in metadata under the given key.

Remove the metadata stored for key.

Replace everything in metadata with the provided Object obj. This can be an empty object. This will throw an exception if the object is not serialisable.

Logger instances are returned by LoggerFactory.getLogger (or window.fhlog.getLogger).

The levels the Logger can be set to. Same as LoggerFactory.LEVELS

Set this Logger to suppress printing logs to th console or stdout/sterr

Detect if this Logger is silent or not. Returns a Boolean

Print a log at DBG level. Works like regular console.debug.

Print a log at INF level. Works like regular console.info.

Print a log at WRN level. Works like regular console.warn.

Print a log at ERR level. Works like regular console.error.

Shorthand for the error method. Deprecated.

Set the level of this logger.

Get the level of this logger.

Get the name of this logger.

Set the name of this logger.

Contributions are always welcome! There is no formal style guide, just follow the style already present in the codebase and be sure to run the tests.

Running the tests will execute them in the Chrome browser and Node.js. You need to accept a FileSystem storage request during this time in Chrome.