Simple utility for unified logging to the console, with optional timestamping.

logger.js

/**
 * Simple utility for unified logging to the console, with optional timestamping.
 *
 * @example // Create several loggers around the application:
 *          var log = logger.create('main');
 *          var logInAnotherModule = logger.create('anotherModule');
 *
 *          // Call the created loggers:
 *          log('Application started');
 *          logInAnotherModule('Module started');
 *
 *          // Produces the following in the console:
 *          // 59.771          [main] Application started logger.js:53
 *          // 59.775 [anotherModule] Module started
 *
 * @author Jarno Rantanen <jarno@jrw.fi>
 * @license http://opensource.org/licenses/MIT
 */
define(function() {

    "use strict";

    var ENABLED = true;
    var TIMESTAMP = true;

    var topLabelLength = 0; // this is shared across the application so that log lines align

    return {

        create: function(label, enabled) {

            enabled = !!enabled || enabled === undefined; // allow enabling/disabling individual loggers
            topLabelLength = window.Math.max(topLabelLength, label.length);

            var boxedLabel = '[' + label + ']';

            /**
             * Main logging method returned by create().  Writes any arguments directly to window.console.
             *
             * @example log('foobar', { baz: 123 });
             *          // => "[main] foobar Object {baz: 123}"
             */
            var logger = function() {

                if (!ENABLED || !enabled || !window.console || !window.console.log) {
                    return;
                }

                var now = new Date();
                var secPadded = now.getSeconds() > 9 ? now.getSeconds() : '0' + now.getSeconds();
                var ms = now.getMilliseconds();
                var msPadded = ms > 99 ? ms : (ms > 9 ? '0' + ms : '00' + ms);
                var timestamp = TIMESTAMP ? (secPadded + '.' + msPadded + ' ') : '';
                var tagPadding = new Array(topLabelLength - label.length + 1).join(' ');
                var argsToLog  = Array.prototype.slice.call(arguments);

                window.console.log.apply(window.console, [ timestamp + tagPadding + boxedLabel ].concat(argsToLog));

            };

            /**
             * Helper for writing out objects.
             *
             * @example log.hash({ herp: 123, derp: 456 });
             *          // => "[main] herp: 123 , derp: 456"
             */
            logger.hash = function(hash) {

                var pieces = [];

                Object.keys(hash).forEach(function(key) {
                    pieces.push(key + ':');
                    pieces.push(hash[key]);
                    pieces.push(',');
                });

                pieces.pop();

                logger.apply(logger, pieces);

            };

            return logger;

        }
    };

});