logger.js

/*!
 * js-logger - http://github.com/jonnyreeves/js-logger
 * Jonny Reeves, http://jonnyreeves.co.uk/
 * js-logger may be freely distributed under the MIT license.
 */

/*jshint sub:true*/
/*global window:true,define:true, module:true*/
(function (window) {
    "use strict";

	// Top level module for the global, static logger instance.
	var Logger = { };

	// For those that are at home that are keeping score.
	Logger.VERSION = "0.9.2";

	// Function which handles all incoming log messages.
	var logHandler;

	// Map of ContextualLogger instances by name; used by Logger.get() to return the same named instance.
	var contextualLoggersByNameMap = {};

	// Polyfill for ES5's Function.bind.
	var bind = function(scope, func) {
		return function() {
			return func.apply(scope, arguments);
		};
	};

	// Super exciting object merger-matron 9000 adding another 100 bytes to your download.
	var merge = function () {
		var args = arguments, target = args[0], key, i;
		for (i = 1; i < args.length; i++) {
			for (key in args[i]) {
				if (!(key in target) && args[i].hasOwnProperty(key)) {
					target[key] = args[i][key];
				}
			}
		}
		return target;
	};

	// Helper to define a logging level object; helps with optimisation.
	var defineLogLevel = function(value, name) {
		return { value: value, name: name };
	};

	// Predefined logging levels.
	Logger.DEBUG = defineLogLevel(1, 'DEBUG');
	Logger.INFO = defineLogLevel(2, 'INFO');
	Logger.WARN = defineLogLevel(4, 'WARN');
	Logger.ERROR = defineLogLevel(8, 'ERROR');
	Logger.OFF = defineLogLevel(99, 'OFF');

	// Inner class which performs the bulk of the work; ContextualLogger instances can be configured independently
	// of each other.
	var ContextualLogger = function(defaultContext) {
		this.context = defaultContext;
		this.setLevel(defaultContext.filterLevel);
		this.log = this.debug;  // Convenience alias.
	};

	ContextualLogger.prototype = {
		// Changes the current logging level for the logging instance.
		setLevel: function(newLevel) {
			// Ensure the supplied Level object looks valid.
			if (newLevel && "value" in newLevel) {
				this.context.filterLevel = newLevel;
			}
		},

		// Is the logger configured to output messages at the supplied level?
		enabledFor: function (lvl) {
			var filterLevel = this.context.filterLevel;
			return lvl.value >= filterLevel.value;
		},

		debug: function () {
			this.invoke(Logger.DEBUG, arguments);
		},

		info: function () {
			this.invoke(Logger.INFO, arguments);
		},

		warn: function () {
			this.invoke(Logger.WARN, arguments);
		},

		error: function () {
			this.invoke(Logger.ERROR, arguments);
		},

		// Invokes the logger callback if it's not being filtered.
		invoke: function (level, msgArgs) {
			if (logHandler && this.enabledFor(level)) {
				logHandler(msgArgs, merge({ level: level }, this.context));
			}
		}
	};

	// Protected instance which all calls to the to level `Logger` module will be routed through.
	var globalLogger = new ContextualLogger({ filterLevel: Logger.OFF });

	// Configure the global Logger instance.
	(function() {
		// Shortcut for optimisers.
		var L = Logger;

		L.enabledFor = bind(globalLogger, globalLogger.enabledFor);
		L.debug = bind(globalLogger, globalLogger.debug);
		L.info = bind(globalLogger, globalLogger.info);
		L.warn = bind(globalLogger, globalLogger.warn);
		L.error = bind(globalLogger, globalLogger.error);

		// Don't forget the convenience alias!
		L.log = L.debug;
	}());

	// Set the global logging handler.  The supplied function should expect two arguments, the first being an arguments
	// object with the supplied log messages and the second being a context object which contains a hash of stateful
	// parameters which the logging function can consume.
	Logger.setHandler = function (func) {
		logHandler = func;
	};

	// Sets the global logging filter level which applies to *all* previously registred, and future Logger instances.
	// (note that named loggers (retrieved via `Logger.get`) can be configured indendently if required).
	Logger.setLevel = function(level) {
		// Set the globalLogger's level.
		globalLogger.setLevel(level);

		// Apply this level to all registered contextual loggers.
		for (var key in contextualLoggersByNameMap) {
			if (contextualLoggersByNameMap.hasOwnProperty(key)) {
				contextualLoggersByNameMap[key].setLevel(level);
			}
		}
	};

	// Retrieve a ContextualLogger instance.  Note that named loggers automatically inherit the global logger's level,
	// default context and log handler.
	Logger.get = function (name) {
		// All logger instances are cached so they can be configured ahead of use.
		return contextualLoggersByNameMap[name] ||
			(contextualLoggersByNameMap[name] = new ContextualLogger(merge({ name: name }, globalLogger.context)));
	};

	// Configure and example a Default implementation which writes to the `window.console` (if present).
	Logger.useDefaults = function(defaultLevel) {
		// Check for the presence of a logger.
		if (!("console" in window)) {
			return;
		}

		var console = window.console;
		Logger.setLevel(defaultLevel || Logger.DEBUG);
		Logger.setHandler(function(messages, context) {
			var hdlr = console.log;

			// Prepend the logger's name to the log message for easy identification.
			if (context.name) {
				Array.prototype.splice.call(messages, 0, 0, "[" + context.name + "]");
			}

			// Delegate through to custom warn/error loggers if present on the console.
			if (context.level === Logger.WARN && console.warn) {
				hdlr = console.warn;
			} else if (context.level === Logger.ERROR && console.error) {
				hdlr = console.error;
			} else if (context.level === Logger.INFO && console.info) {
				hdlr = console.info;
			}

			hdlr.apply(console, messages);
		});
	};


    // Export to popular environments boilerplate.
    if (typeof define === 'function' && define.amd) {
        define(Logger);
    }
    else if (typeof module !== 'undefined' && module.exports) {
        module.exports = Logger;
    }
    else {
        window['Logger'] = Logger;
    }
}(window));