Override console.log (or any function in general): Is there a proper way to do this?

Question

I find myself doing this quite often both on the browser and in node.js and it's about time I came up with a proper way to do this without debugging it for a while each time.

Here's what I'm currently working on (this is node.js):

var log4js = require("log4js");

log4js.loadAppender('file');
log4js.addAppender(log4js.appenders.file('log.log'));
var logger = log4js.getLogger();
console.log = function () {
    logger.debug.apply(logger, Array.prototype.slice.call(arguments));
};

This is basically a monkey patch to take console.logging code and turn it into proper logging code.

I'm not sure if this is something proper or completely asinine.

Conceptually, I am forcing arguments sent to console.log into an array, which then is passed to apply. All of this is to work around the fact that I don't know how to declare a variadic function in JS. (perhaps this is the canonical way to do so).

Perhaps the same can be achieved with console.log = logger.debug. Oh well, I want to know how I can pass the arguments.

For instance, there are certain things of this sort that won't work for whatever reason in the browser (but does in node):

var l = console.log;
l('hello');

Granted, this is not the same as overriding console.log, this is just to shorten the name of it, but still.

Ah, I actually realized what's wrong here: This will work.

l.call(console, 'hello');

Which means it's just missing a bit of finagling with this.

If you are still looking for the actual question of this question look at the italicized line above.

Answer 1

I'm not sure if this is something proper or completely asinine.

For your own projects, it should be fine. Though, I would probably refrain from modifying Node's documented API (beyond the few parts that suggest modification) for any projects you intend to distribute on NPM.

---

Currently, .apply() is the only way to specify a collection as the arguments to a function call.

logger.debug.apply(logger, Array.prototype.slice.call(arguments));

Though, ECMAScript 6 will be introducing the spread operator as an alternative.

logger.debug(...arguments);

However, the slice probably isn't necessary, since it isn't modifying the collection before passing it.

logger.debug.apply(logger, arguments);

---

As for l('hello'), you can use .bind() to ensure the context.

var l = console.log.bind(console);
l('hello');

Though, this does depend on what version of a particular engine you're using. With Node 0.10.15 and Chrome 28, console.log is already bound to console. So, the snippet you listed wouldn't throw an error.