Consequences of Dynamically rewriting a function in javascript?

Question

In javascript, you can rewrite a function, like so:

function foo() { 
   setTimeout(function() {
        alert('sup stallion');
        foo = function() { //rewrite foo to nolonger wait 4 seconds to alert.
             alert('sup stallion');
        }
   }, 4000);
}

Obviously this is a contrived example, but is there anything conceptually wrong with this approach (other than a race condition).

Answer 1

Self modifying code can be confusing, and hard to debug, so it's generally avoided.

Other than that there is no problem, and no race condition either.

Answer 2

One thing I noticed while testing your code. Consider this:

setInterval(foo, 6000);

Function foo is being passed to setInterval before it was modified, and the original foo will run every 6 seconds, even after the binding has been updated.

On the other hand, the code below will run the original function only on the first call (which updates the binding). Subsequent calls will invoke the updated version:

setInterval(function(){foo();}, 6000);

Looks obvious, but could be hard to debug...