move cache assignment to toPrimitive call

Author: bmeck

lib/timers.js

@@ -151,7 +151,6 @@ const KNOWN_TIMERS = Object.create(null);
 // Schedule or re-schedule a timer.
 // The item must have been enroll()'d first.
 const active = exports.active = function(item) {
-  KNOWN_TIMERS[item[async_id_symbol]] = item;
   insert(item, false);
 };
 
@@ -537,7 +536,9 @@ function unrefdHandle(timer, now) {
 }
 
 Timeout.prototype[Symbol.toPrimitive] = function() {
-  return this[async_id_symbol];
+  const id = this[async_id_symbol];
+  KNOWN_TIMERS[id] = this;
+  return id;
 };
 
 Timeout.prototype.unref = function() {