I once used the Python function "gc.get_objects()", which returns a list of all objects in memory, to diagnose a memory leak. I don't suppose anything like it exists in JS tooling?
You can capture a heap snapshot in most browsers now using development tools. However, even a blank webpage (about:blank) has tens of thousands of objects allocated for the default JavaScript/DOM APIs. It's challenging to manually grok a JavaScript heap.
The approach I used was to take a snapshot, count up all the different object types (making a hash table mapping "name of type of object" => "count of objects whose type has that name", then discarding the snapshot), then take another snapshot a few minutes later, and see what the difference was, and which type of object there was suddenly a lot more of. Then I looked at various instances of that object. It turned out to be some async queue-related object that was only used in a couple of places, so that narrowed it down a lot. Even if it were something generic like a hash table or list, I suspect looking at instances of the object and breaking them down by some observable quality (e.g. number of elements, the set of keys in a table, the types of objects in a list), plus the differential approach, will take you fairly far.
There are some browser-specific tools that will do something like that out-of-band (e.g. in Firefox about:memory has a "Save GC & CC logs" option that outputs data about what the GC and cycle collector heap graphs look like). But interpreting those graphs is not easy, sadly.
