logger.js

var logger = function(level){
    this.logs = [];
    //note: set level based on production or dev
    this.level = level || 3; //1 = verbose, 2 = warning, 3 = error
    
    //internal log method
    this._log = function(level, message) {
        //note: if level == 2 you could do console.warn (and remove Log Level 2:)
        //note: if level == 3 you could do console.error (and remove Log Level 3:)
        console.log(["Log level ", level, ": ", message].join(""));
    }
};
logger.prototype.log = function (level) {
    var message = Array.prototype.join.call(Array.prototype.slice.call(arguments, 1), " ");
    if (level <= this.level) {
        this._log(message);
        return;
    }
    this.logs.push({level: level, message: message});
    //todo: this should instead keep an internal "index" and then just increment that instead of checking and splicing
    if (this.logs.length > 50) { //onlyt keep 50 logs around
        this.logs = this.logs.slice(-50);
    }
};

logger.prototype.setLogLevel = function (level) {
    if (level == this.level) {
        return;
    }
    //now that they changed the level, print out any logs from the last 50 that match this log level
    var skippedLogs = [];
    for (var i = 0, l = this.logs.length; i < l; i++) {
        if (this.logs[i].level > level) {
            skippedLogs.push(this.logs[i]);
            continue;
        }
        this._log(this.logs[i].message);
    }
    this.logs = skippedLogs;
};
window.logger = logger;

var noop = function() {};
if (!window.console) {
    //ie sucks
    window.console = {
        log: noop,
        warn: noop,
        error: noop
    };
} else if (!console.log) {
    //if they don't have log for some reason, they won't have any
    console.log = noop;
    console.warn = noop;
    console.error = noop;
}

usage.js

window.myLogger = new logger(2);
myLogger.log(1, "This is a log message");
myLogger.log(1, "This is a log message with a", variable, "spaces will automatically be added");