From c2ed6e21d6c525e5da14c8a24278bba5dd9253e1 Mon Sep 17 00:00:00 2001
From: "JiaLi.Passion" <JiaLi.Passion@gmail.com>
Date: Tue, 22 May 2018 23:49:02 +0900
Subject: [PATCH] feat(Core): fix #910, add a flag to allow user to ignore
 duplicate Zone error

---
 lib/zone.ts | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/zone.ts b/lib/zone.ts
index 9cbd04fdc..1e4fd2d07 100644
--- a/lib/zone.ts
+++ b/lib/zone.ts
@@ -645,7 +645,19 @@ const Zone: ZoneType = (function(global: any) {
   }
   mark('Zone');
   if (global['Zone']) {
-    throw new Error('Zone already loaded.');
+    if (global[('__zone_symbol__ignoreDuplicateZoneCheck')] === true && typeof global['Zone'].__symbol__ === 'function') {
+      // if global['Zone'] already exists (maybe zone.js was already loaded or
+      // some other lib also registered a global object named Zone), we may need
+      // to throw an error, but sometimes user may not want this error.
+      // For example,
+      // we have two web pages, page1 includes zone.js, page2 doesn't.
+      // and the 1st time user load page1 and page2, everything work fine,
+      // but when user load page2 again, error occurs because global['Zone'] already exists.
+      // so we add a flag to let user choose whether to throw this error or not.
+      return;
+    } else {
+      throw new Error('Zone already loaded.');
+    }
   }
 
   class Zone implements AmbientZone {