GCIntegration - SpiderMonkey Redirect 1
a very simple way to identify weak pointers is to look for usage of js_isabouttobefinalized().
... if a pointer is weak, there's a good chance that js_isabouttobefinalized() is used to null it out if its referent is about to be finalized.
...it's likely that js_isabouttobefinalized() will also be changed to take the address of the pointer.

JS_SetGCCallback
the callback may use js_isabouttobefinalized to clean up weak references to js objects (that is, pointers that are not traced by the gc).

JSAPI reference
rmonkey 38 enum jsfinalizestatus added in spidermonkey 17 js_removefinalizecallback added in spidermonkey 38 js_setgczeal added in spidermonkey 1.8 js_schedulegc added in spidermonkey 17 js_dumpheap added in spidermonkey 1.8 js_setgccallbackrt obsolete since jsapi 13 js_setfinalizecallback added in spidermonkey 17 obsolete since jsapi 32 js_markgcthing obsolete since jsapi 5 js_isabouttobefinalized obsolete since jsapi 35 js_clearnewbornroots obsolete since jsapi 5 the rest of these apis help protect objects from being destroyed by the garbage collector before the application is done using them.

SpiderMonkey 38
1100579) js_evaluateucscript (bug 1100579) js_executescriptversion (bug 1095660) js_getflatstringchars (bug 1037869) js_getfunctioncallback (bug 1103269) js_getinternedstringchars (bug 1037869) js_getinternedstringcharsandlength (bug 1037869) js_getstringcharsandlength (bug 1037869) js_getstringcharsz (bug 1037869) js_getstringcharszandlength (bug 1037869) js_gettypename (bug 1037718) js_isabouttobefinalized (bug 650161) js_lookupelement (bug 1094176) js_lookupproperty (bug 1094176) js_lookuppropertybyid (bug 1094176) js_lookupucproperty (bug 1094176) js_newpropertyiterator (bug 1081660) js_nextproperty (bug 1081660) js_resolvestub (bug 1103152) js_setfinalizecallback (bug 996785) js_setfunctioncallback (bug 1103269) jschar (bug 1063962) api changes jschar, a typedef for the standard c++...