diff --git a/lib/mixins/property-effects.js b/lib/mixins/property-effects.js
index bb4b1f9165..9fa0304842 100644
--- a/lib/mixins/property-effects.js
+++ b/lib/mixins/property-effects.js
@@ -96,6 +96,7 @@ function ensureOwnEffectMap(model, type, cloneArrays) {
     if (cloneArrays) {
       for (let p in effects) {
         let protoFx = effects[p];
+        // Perf optimization over Array.slice
         let instFx = effects[p] = Array(protoFx.length);
         for (let i=0; i<protoFx.length; i++) {
           instFx[i] = protoFx[i];