garbage collection for javascript

I have two piece of code sample 1

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(function(){

var x = 1;

 this.getx = function() { return x; };

})();

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sample 2

(function(){

var x = 1;

 this.getx = function() { };

})();

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both code samples create a closure, x in sample one is referenced, while x in sample two is not referenced, I know x in sample one will not be garbage collected, my question will x in sample two be garbage collected?

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The ECMAScript standard is intentionally silent on how the garbage collector should work so implementations are likely to differ. However, in general, if an object is not referencible from a live object it will be collected.

In sample 2 it means that the closure will likely be collected but it is also likely a closure will not even be created since the function does not reference it. Closures are expensive and modern JavaScript engines try to avoid creating them unless they are forced to.

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Garbage collection in Javascript is a nebulous thing. Generally speaking, you can assume (though we know what assuming does) that once there are no references to a variable (eg, once it goes out of scope), it will be garbage collected. However, your closures will not work as you intend because they are not assigned to anything; thus you will have no function object to call getx() on. If you were to assign it, though, x would never be out of scope unless you used the delete keyword on any variables holding the function reference.

Simple rule: use the delete operator whenever you're concerned about collection - this will remove the reference, and it's more likely that the memory will be freed.

Edit: comments by @chuckj aside, whether you use delete or assign the variable to undefined still lends to the point that you want to get the reference count to 0 if there's to be any hope of freeing the memory.

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To modern browsers, x in sample two will be garbage collected in most browsers, except for ie6