From c0ce2523f0bfd7325c8dda3eb2c1acd9a4c0599c Mon Sep 17 00:00:00 2001
From: aleclarson <alec.stanford.larson@gmail.com>
Date: Thu, 13 Dec 2018 21:17:06 -0500
Subject: [PATCH] perf(proxy): deletion of an undeclared property

---
 src/proxy.js | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/proxy.js b/src/proxy.js
index 64076b73..24129376 100644
--- a/src/proxy.js
+++ b/src/proxy.js
@@ -107,9 +107,12 @@ function set(state, prop, value) {
 }
 
 function deleteProperty(state, prop) {
-    state.assigned[prop] = false
-    markChanged(state)
-    delete state.copy[prop]
+    // The `undefined` check is a fast path for pre-existing keys.
+    if (state.base[prop] !== undefined || prop in state.base) {
+        state.assigned[prop] = false
+        markChanged(state)
+    }
+    if (state.copy) delete state.copy[prop]
     return true
 }
 
@@ -117,8 +120,8 @@ function getOwnPropertyDescriptor(state, prop) {
     const owner = state.modified
         ? state.copy
         : has(state.proxies, prop)
-            ? state.proxies
-            : state.base
+        ? state.proxies
+        : state.base
     const descriptor = Reflect.getOwnPropertyDescriptor(owner, prop)
     if (descriptor && !(Array.isArray(owner) && prop === "length"))
         descriptor.configurable = true