I observe a node by simply doing

new MutationObserver(callback)
  .observe(shape.node, {attributes: true})

As you can see I dont have any references to the observer. The observed node will get destroyed at some point.

Is the memory for the node and for the observer cleaned up? Or do they keep themselves alife? And if so: How can I prevent that from happening? I do not know when the node gets removed.

Ofc I could also observe the parent and disconnect the first observer when the parent has a "child list changed" observed but I would like to avoid that

I observe a node by simply doing

new MutationObserver(callback)
  .observe(shape.node, {attributes: true})

As you can see I dont have any references to the observer. The observed node will get destroyed at some point.

Is the memory for the node and for the observer cleaned up? Or do they keep themselves alife? And if so: How can I prevent that from happening? I do not know when the node gets removed.

Ofc I could also observe the parent and disconnect the first observer when the parent has a "child list changed" observed but I would like to avoid that

• javascript
• mutation-observers

• MDN says it will be GC'd. – woxxom Commented Jun 12, 2018 at 15:52
• @wOxxOm I read through it mutiple times now but it seems I am blind - cant find it :/ – Fuzzyma Commented Jun 12, 2018 at 16:07
• 4 I gave the wrong link, should've been to MO#disconnect(). – woxxom Commented Jun 12, 2018 at 16:56
• Ah, there it is! Thank you very much! – Fuzzyma Commented Jun 12, 2018 at 19:09

1 Answer 1

MutationObservers hold a weak reference to the nodes they are observing, and the nodes have a strong reference to the mutation observer. That means that in your case, the only thing referencing the observer is the node object. If the node is GCed, nothing will be referencing the observer so it will also be GCed.

See DOM Specification section 4.3.4. Garbage collection, which states:

Nodes have a strong reference to registered observers in their registered observer list.

Registered observers in a node’s registered observer list have a weak reference to the node.