how to extend a method in javascript?

Question

I want to add additional functionality to a method, for instance:

console.log()

so the original 'log' functionality is retained, and I can get it to do something new as well. Is this possible? I've read a few bits on using prototype but haven't quite grasped it.

Many thanks,

Answer 1

It's very easy. If you want your new log mehod to be in place of the old log method just do something like that:

console._log = console.log; // just backing up old log method
console.log = function(){
    console._log(arguments);
    alert("I'm doing something else here");     
}
console.log(console);

---

UPDATE:

All the solutions presented, including mine, didn't reproduced the log behavior perfectly as @TomBates stated. The output differed because arguments were being logged wrapped in an object instead of passed separately. The only way I could find to reproduce the behavior of the old log + the extending functionality was doing this:

    console.log(window, this, console); // old log in action

console._log = console.log; // just backing up old log method
console.log = function(){
    var args_string = '';
    for(i in arguments){
        if(arguments.hasOwnProperty(i)){
            args_string += 'arguments['+ i + ']';
            if(i != arguments.length - 1){
                args_string += ',';
            } 
        }
    }
    var expression = 'console._log(' + args_string + ');';
    eval(expression);

    alert("I'm doing something else here"); 
    // your dazzling method extension here   
}

console.log(window, this, console); //new log in action

Not so elegant, but works as expected. the outputs of both old log and new log are now identical.