javascript V8 optimisation and “leaking arguments”

Question

I read in various places that it\'s advisable to be careful with the arguments object and that this is ok...

    var i = arguments.length, args = ne         


        

Answer 1

This is a 2-fold problem:

1. You lose any and all possible optimizations and branch predictions
   The arguments object is unpredictible.
2. You leak memory. Really bad!

Consider the following code (run it at your own risk!):

function a(){return arguments;}

x=a(document.getElementsByTagName('*'));

window._interval=setInterval(function(){

    for(var i=0;i<1e6;i++)
    {
        x=a(x);
    }
},5000);

*{font-family:sans-serif;}

Warning! This may overheat your cpu and crash your browser really badly!

I'm not responsible for any software and hardware damages!

Run at your own risk!!!

If you ran this code, press F5 to stop or close the browser.

If you want, you can try to stop it. (the RAM may remain unchanged)

And now watch your RAM go up, when you run that (it goes up at a rate of around 300-500MB every 5 seconds).
A naive implementation that simply passes the arguments around may cause these problems.

Not to mention that your code will (generally) be a tad slower.

---

Note that this:

function a(){return arguments;}
function b(arg){return arg;}

x=a(document.getElementsByTagName('*'));

window._interval=setInterval(function(){

    for(var i=0;i<1e6;i++)
    {
        x=b(x);
    }
},5000);

*{font-family:sans-serif;}

This may be safe, but be careful!

I'm not responsible for any software and hardware damages!

Run at your own risk!!!

If you ran this code, press F5 to stop or close the browser.

If you want, you can try to stop it.

Won't have the same effect as the code before.
This is because b() returns the same variable, instead of a new reference to a new arguments object.
This is a very important difference.