This page is for analyzing JSON dumps of the GC heap. To debug an issue that you think might be a leaked or abandoned object (often a Document or JSGlobalObject), load the test page, then navigate to about:blank or other simple page. Now simulate a memory warning (to clear the page cache) by issuing the following command in a Terminal window:
notifyutil -p org.WebKit.lowMemory
You can now inspect the list of live documents via:
notifyutil -p com.apple.WebKit.showAllDocuments
which prints its output to the system log. If this lists documents other than the current page, you may have a leaked or abandoned Document. To see if the GC heap is referencing that Document, obtain a GC heap dump:
notifyutil -p com.apple.WebKit.dumpGCHeap
That command will generate a JSON file in /tmp (or equivalent); the file path is dumped to the system log. Drag that file onto the drop target in the top right (or use the ?filename= URL parameter).
For more information, see the wiki page on Inspecting the GC heap.