log.js

var log = (function() {
    'use strict';

    var log = {};
    
    log.Level = function (level, name) {
        this.level = level;
        this.name = name;
    };
    
    log.Level.prototype.toString = function () {
        return this.name;
    };
    
    var levels = [
        {name: 'error', type: 'error'},
        {name: 'warn', type: 'warn'},
        {name: 'info', type: 'log'},
        {name: 'debug', type: 'log'},
        {name: 'trace', type: 'log'}
    ];
    for (var i = 0; i < levels.length; i++) {
        var obj = new log.Level((i + 1) * 10, levels[i].name.toUpperCase());
        log.Level[levels[i].name.toUpperCase()] = obj;
        levels[i].obj = obj;
    }
    log.Level.OFF = new log.Level(Number.MIN_VALUE, 'OFF');
    log.Level.ALL = new log.Level(Number.MAX_VALUE, 'ALL');
    
    var bind;
    if (typeof Function.prototype.bind === 'function') {
        bind = function (type, prefix) {
            return console[type].bind(console, prefix);
        };
    } else {
        bind = function (type, prefix) {
            return function () {
                [].unshift.call(arguments, prefix);
                console[type].apply(console, arguments);
            };
        };
    }
    
    log.Logger = function (name, level) {
        this.name = name;
        this.level = level;
        this.reinit();
    };
    
    log.Logger.prototype.reinit = function () {
        for (var i = 0; i < levels.length; i++) {
            var d = levels[i];
            this[d.name] = (d.obj.level <= this.level.level)
                ? bind(d.type, '[' + this.name + ':' + d.obj.name + ']')
                : function () {};
        }
    };
    
    return log;
})();