loglevel.js

/*! loglevel - v1.2.0 - https://github.com/pimterry/loglevel - (c) 2014 Tim Perry - licensed MIT */
(function (root, definition) {
    if (typeof module === 'object' && module.exports && typeof require === 'function') {
        module.exports = definition();
    } else if (typeof define === 'function' && typeof define.amd === 'object') {
        define(definition);
    } else {
        root.log = definition();
    }
}(this, function () {
    var self = {};
    var noop = function() {};
    var undefinedType = "undefined";

    function realMethod(methodName) {
        if (typeof console === undefinedType) {
            return false; // We can't build a real method without a console to log to
        } else if (console[methodName] !== undefined) {
            return bindMethod(console, methodName);
        } else if (console.log !== undefined) {
            return bindMethod(console, 'log');
        } else {
            return noop;
        }
    }

    function bindMethod(obj, methodName) {
        var method = obj[methodName];
        if (typeof method.bind === 'function') {
            return method.bind(obj);
        } else {
            try {
                return Function.prototype.bind.call(method, obj);
            } catch (e) {
                // Missing bind shim or IE8 + Modernizr, fallback to wrapping
                return function() {
                    return Function.prototype.apply.apply(method, [obj, arguments]);
                };
            }
        }
    }

    function enableLoggingWhenConsoleArrives(methodName, level) {
        return function () {
            if (typeof console !== undefinedType) {
                replaceLoggingMethods(level);
                self[methodName].apply(self, arguments);
            }
        };
    }

    var logMethods = [
        "trace",
        "debug",
        "info",
        "warn",
        "error"
    ];

    function replaceLoggingMethods(level) {
        for (var i = 0; i < logMethods.length; i++) {
            var methodName = logMethods[i];
            self[methodName] = (i < level) ? noop : self.methodFactory(methodName, level);
        }
    }

    function persistLevelIfPossible(levelNum) {
        var levelName = (logMethods[levelNum] || 'silent').toUpperCase();

        // Use localStorage if available
        try {
            window.localStorage['loglevel'] = levelName;
            return;
        } catch (ignore) {}

        // Use session cookie as fallback
        try {
            window.document.cookie = "loglevel=" + levelName + ";";
        } catch (ignore) {}
    }

    function loadPersistedLevel() {
        var storedLevel;

        try {
            storedLevel = window.localStorage['loglevel'];
        } catch (ignore) {}

        if (typeof storedLevel === undefinedType) {
            try {
                storedLevel = /loglevel=([^;]+)/.exec(window.document.cookie)[1];
            } catch (ignore) {}
        }
        
        if (self.levels[storedLevel] === undefined) {
            storedLevel = "WARN";
        }

        self.setLevel(self.levels[storedLevel]);
    }

    /*
     *
     * Public API
     *
     */

    self.levels = { "TRACE": 0, "DEBUG": 1, "INFO": 2, "WARN": 3,
        "ERROR": 4, "SILENT": 5};

    self.methodFactory = function (methodName, level) {
        return realMethod(methodName) ||
               enableLoggingWhenConsoleArrives(methodName, level);
    };

    self.setLevel = function (level) {
        if (typeof level === "string" && self.levels[level.toUpperCase()] !== undefined) {
            level = self.levels[level.toUpperCase()];
        }
        if (typeof level === "number" && level >= 0 && level <= self.levels.SILENT) {
            persistLevelIfPossible(level);
            replaceLoggingMethods(level);
            if (typeof console === undefinedType && level < self.levels.SILENT) {
                return "No console available for logging";
            }
        } else {
            throw "log.setLevel() called with invalid level: " + level;
        }
    };

    self.enableAll = function() {
        self.setLevel(self.levels.TRACE);
    };

    self.disableAll = function() {
        self.setLevel(self.levels.SILENT);
    };

    // Grab the current global log variable in case of overwrite
    var _log = (typeof window !== undefinedType) ? window.log : undefined;
    self.noConflict = function() {
        if (typeof window !== undefinedType &&
               window.log === self) {
            window.log = _log;
        }

        return self;
    };

    loadPersistedLevel();
    return self;
}));