Is it possible to create a "weak reference" in javascript?

Question

Is there any way in javascript to create a "weak reference" to another object? Here is the wiki page describing what a weak reference is. Here is another article that describes them in Java. Can anyone think of a way to implement this behavior in javascript?

Answer 1

http://www.jibbering.com/faq/faq_notes/closures.html

ECMAScript uses automatic garbage collection. The specification does not define the details, leaving that to the implementers to sort out, and some implementations are known to give a very low priority to their garbage collection operations. But the general idea is that if an object becomes un-referable (by having no remaining references to it left accessible to executing code) it becomes available for garbage collection and will at some future point be destroyed and any resources it is consuming freed and returned to the system for re-use.

This would normally be the case upon exiting an execution context. The scope chain structure, the Activation/Variable object and any objects created within the execution context, including function objects, would no longer be accessible and so would become available for garbage collection.

Meaning there are no weak ones only ones that no longer become available.

Answer 2

There is no language support for weakrefs in JavaScript. You can roll your own using manual reference counting, but not especially smoothly. You can't make a proxy wrapper object, because in JavaScript objects never know when they're about to be garbage-collected.

So your ‘weak reference’ becomes a key (eg. integer) in a simple lookup, with an add-reference and remove-reference method, and when there are no manually-tracked references anymore then entry can be deleted, leaving future lookups on that key to return null.

This is not really a weakref, but it can solve some of the same problems. It's typically done in complex web applications to prevent memory leakage from browsers (typically IE, especially older versions) when there is a reference loop between a DOM Node or event handler, and an object associated with it such as a closure. In these cases a full reference-counting scheme may not even be necessary.

Answer 3

Just for reference; JavaScript doesn't have it, but ActionScript 3 (which is also ECMAScript) does. Check out the constructor parameter for Dictionary.