Can I trigger JavaScript's garbage collection?

Question

I want to trigger JavaScript garbage collection. Is it possible? Why would I want to, or not want to, do this?

Answer 1

I went out on a small journey to seek an answer to one of your questions: Is it possible?

People all over town are saying that deleting the references will do the trick. Some people say that wiping the object is an extra guarantee (example). So I wrote a script that will try every trick in the book, and I was astonished to see that in Chrome (22.0.1229.79) and IE (9.0.8112.16421), garbage collection doesn't even seem to work. Firefox (15.0.1) managed without any major drawbacks apart from one (see case 4f down below).

In pseudo-code, the test goes something like this.

1. Create a container, an array, that will hold objects of some sort. We'll call this container Bertil here on.

2. Each and every object therein, as an element in Bertil, shall have his own array-container declared as a property. This array will hold a whole lot of bytes. We'll call any one of Bertil's elements, the object, Joshua. Each Joshua's byte array will be called Smith.

   Here's a mind map for you to lean back on:

   Bertil [Array of objects] -> Joshua [Object] -> Smith [Array of bytes] -> Unnamed [Bytes].

3. When we've made a mess out of our available memory, hang around for a sec or two and then execute any one of the following "destruction algorithms":

   4a. Throw a delete operand on the main object container, Bertil.

   4b. Throw a delete operand on each and every object in that container, kill every Joshua alive.

   4c. Throw a delete operand on each and every array of bytes, the Smiths.

   4d. Assign NULL to every Joshua.

   4e. Assign UNDEFINED to every Joshua.

   4f. Manually delete each and every byte that any Joshua holds.

   4g. Do all of the above in a working order.

So what happened? In case 4a and 4b, no browser's garbage collector (GC) kicked in. In case 4c to 4e, Firefox did kick in and displayed some proof of concept. Memory was reclaimed shortly within the minute. With current hardcoded default values on some of the variables used as test configuration, case 4f and 4e caused Chrome to hang, so I can't draw any conclusions there. You are free to do your own testing with your own variables, links will be posted soon. IE survived case 4f and 4e but his GC was dead as usual. Unexpectedly, Firefox survived but didn't pass 4f. Firefox survived and passed 4g.

In all of the cases when a browser's GC failed to kick in, waiting around for at least 10 minutes didn't solve the problem. And reloading the entire page caused the memory footprint to double.

My conclusion is that I must have made a horrible error in the code or the answer to your question is: No we can't trigger the GC. Whenever we try to do so we will be punished severely and we should stick our heads in the sand. Please I encourage you to go ahead, try these test cases on your own. Have a look in the code were comment on the details. Also, download the page and rewrite the script and see if you can trigger the GC in a more proper way. I sure failed and I can't for the life of me believe that Chrome and IE doesn't have a working garbage collector.

http://martinandersson.com/dev/gc_test/?case=1

http://martinandersson.com/dev/gc_test/?case=2

http://martinandersson.com/dev/gc_test/?case=3

http://martinandersson.com/dev/gc_test/?case=4

http://martinandersson.com/dev/gc_test/?case=5

http://martinandersson.com/dev/gc_test/?case=6

http://martinandersson.com/dev/gc_test/?case=7

Answer 2

You can trigger manually JavaScript garbage collector in IE and Opera, but it's not recommended, so better don't use it at all. I give commands more just for information purpose.

Internet Explorer:

window.CollectGarbage() 

Opera 7+:

window.opera.collect()