Question

var f = function() {
    // Do something useful here
};

Is there a way to ‘observe’ this function, and get notified when it is executed? Something similar to bind in jQuery, but I want to bind functions and not dom events?

I don’t want something like this:

var f = function() {
    // Do something useful here
    notifyObserver();
};

but I want something like this:

f.bind(function() {
    alert('F was executed.');
});

Answer 1

You could replace f with a function that calls notifyObserver:

f = (function(oldF){
      return function(){
        notifyObserver(); 
        oldF(); 
      }; 
    })(f);

That way you don’t need to modify (the old) f itself. This doesn’t include your bind functionality, of course. I’d probably create some kind of manager class for this where you can register event handlers

manager.bind('f', function(){...});

And creating the wrapper function would look more like

f = (function(oldF){
      return function(){
        manager.notify('f');
        oldF(); 
      }; 
    })(f);

You can generalize the creation of the wrapper:

function wrap(methodToWrap, eventName){
    return function(){
        manager.notify(eventName);
        return methodToWrap.apply(this, arguments);
    }
}

(This works with any number of arguments and return values!)

And then do something like:

f = wrap(f, "f");

See: http://jsfiddle.net/NBefc/2/ (updated, no with return values)