closures and memory leaks

allworknoplay · 04-23-2009, 02:46 PM

JS closures is still a little bit beyond my understanding but in this article I am reading, I just don't see what the author is pointing out...

He says:

Quote:

Even defining the simplest of functions can create closures:

Code:

var x = 5;
var n = function(){
    y=10;
    return y;
}

Quote:

It doesn't seem like we are creating a closure here, but we are. Why? When we create our function it gets a reference to all variables in its current scope, so we are creating a new reference to our x variable.

Now I keep staring at that code, and I don't see what he's talking about? The function has only one variable in it's scope, and that's the Y variable in which he returns it.

How does that have any affect at all on the X variable?

I am reading it from here:

http://www.htmlgoodies.com/primers/j...le.php/3606701

Wildhoney · 04-23-2009, 04:59 PM

I assume what he's attempting to say is that both x and n contain the function which returns y. However, x.toString() appears to show 5 to me, which I'd expect.

If x were a reference to n then that'd be expected behaviour, but it isn't, and so I don't understand why he's telling us that.

Perhaps somebody else has a better idea.

Salathe · 04-23-2009, 05:39 PM

Quote:

Originally Posted by allworknoplay

Now I keep staring at that code, and I don't see what he's talking about? The function has only one variable in it's scope, and that's the Y variable in which he returns it.

Sure, there's only one variable used (aside: not declared) inside the function but the variable x is still available to be used. For example:

JavaScript Code:

var x = 5;
var n = function(){
    var y = 10;
    return x + y;
};

// … some time later
x = 113;
alert(n()); // 123

sketchMedia · 04-24-2009, 11:36 AM

He may be trying to show that top level variables are automatically made global (because JS has no linker, so throws it all into a global namespace), thus setting the stage to explain cyclic references in closures and why they happen.

I may be wrong ofc.