Etcher

A flexible logging library for javascript.

Creating a Logger

To start logging, create a new Etcher object by passing a handler to its constructor.

var Etcher = require('etcher');
var ConsoleLogHandler = require('etcher').handler.ConsoleLogHandler;

var logger = new Etcher(new ConsoleLogHandler());

Log Levels

Etcher uses the log levels dictated by RFC 5424: The Syslog Protocol.

• emergency: system is unusable
• alert: action must be taken immediately
• critical: critical conditions
• error: error conditions
• warning: warning conditions
• notice: normal but significant condition
• info: informational messages
• debug: debug-level messages

Logging

There are several ways to create a log. There are methods for each log level as well as a log method.

Log Level Methods

The log level methods are a quick shortcut for creating a log with a specific log level. Each log level method takes two arguments, and message and an optional log context object.

logger.critical('something bad happened', {foo: 'relevant info'});
logger.alert('take immediate action!');

The log Method

The log method allows passing a log level as an argument. This is useful for cases where the log level is determined dynamically.

logger.log('info', 'an informational message', {data: 'some useful data'});

The Log Object

Internally, whenever a log method is called, Etcher creates a Log object which it passes to its log handler. You can also create a Log object manually to pass to the log method.

The Log constructor takes 3 arguments: the log level, the log message, and an optional context;

var notice = new Log('notice', 'an interesting thing happened', {foo: 'foo'});
logger.log(notice);

See Log.js for full documentation.

Multiple Handlers

A single Etcher instance can have an unlimited number of log handlers by using a ChainLogHandler. In this first case, all log handlers will be called every time a log is created.

var logger = new Etcher(new Etcher.handler.ChainLogHandler([
    new Etcher.handler.ConsoleLogHandler(),
    new MyCustomHandler()
]));

The ChainLogHandler can take a second argument called bubble. If it is true, it will stop handling a log as soon as it is handled successfully.

var logger = new Etcher(new Etcher.handler.ChainLogHandler([
    new LogSometimesHandler(),
    new BackupHandler()
]), true);

In this case, the LogSometimesHandler will be called first, and it it fails, BackupHandler will be called.

The Log Context

The last argument passed to the logging methods is the "context". This is just an object of information related to the log. If the context is not a plain javascript object, it will be converted to an object with a value property.

Logging Error Objects

There are a couple shortcuts for logging errors. If an Error object is passed as the context, it will be converted to a plain object with an error property. If an Error is passed as the message parameter, the context error property will be set, and the message will be set to the error message string.

Custom Handlers

Etcher is designed to be customizable. You can create your own custom log handlers by just creating an object with a boolean handle(Log log) method. It should return true if the log was handled successfully, and false if it was not handled.

var alertHandler = {
    handle: function(log) {
        alert(log.getMessage());
        return true;
    }
};

You can also use a constructor function to create a more robust handler.

function AlertHandler(alertFunction) {
    this._alertFunction = alertFunction;
}

AlertHandler.prototype.handle = function(log) {
    this._alertFunction(log.getMessage());
    return true;
};

var alertHandler = new AlertHandler(window.alert);