JS_TracerInit
in the latter case, the only operations the callback may perform on thing are to call js_tracechildren or the debug-only js_printtracethinginfo function.

JSAPI reference
onkey 1.8 obsolete since jsapi 26 js_call_tracer added in spidermonkey 1.8 obsolete since jsapi 23 js_call_value_tracer added in spidermonkey 1.8 obsolete since jsapi 23 js_call_object_tracer added in spidermonkey 1.8 obsolete since jsapi 23 js_call_string_tracer added in spidermonkey 1.8 obsolete since jsapi 23 js_call_double_tracer added in spidermonkey 1.8 obsolete since javascript 1.8.5 js_printtracethinginfo (debug-only) added in spidermonkey 1.8 obsolete since jsapi 16 miscellaneous gc apis: js_updatemalloccounter added in spidermonkey 17 js::setlargeallocationfailurecallback added in spidermonkey 31 js::setoutofmemorycallback added in spidermonkey 31 js_enumeratediagnosticmemoryregions added in spidermonkey 17 jsval_lock obsolete since jsapi 18 jsval_unlock obsolete since jsapi 18 js_...