don't use MutationObserver in iOS completely, fixes #455, #339

CHANGELOG.md

@@ -103,6 +103,7 @@
   - Fix non-enumerable integer keys issue because of Nashorn ~ JDK8 bug, [#389](https://github.com/zloirock/core-js/issues/389).
   - Fix [Safari 12.0 `Array#reverse` bug](https://bugs.webkit.org/show_bug.cgi?id=188794).
   - Fix buggy `String#padStart` and `String#padEnd` mobile Safari implementations, [#414](https://github.com/zloirock/core-js/issues/414).
+  - One more fix for microtasks in iOS related [#339](https://github.com/zloirock/core-js/issues/339).
   - Added a fallback for [Rhino bug](https://github.com/mozilla/rhino/issues/346), [#440](https://github.com/zloirock/core-js/issues/440).
 - Repository:
   - Change `core-js` repository structure to monorepo with packages in `/packages/` directory.

packages/core-js/internals/microtask.js

@@ -1,7 +1,8 @@
 var global = require('../internals/global');
 var classof = require('../internals/classof-raw');
 var macrotask = require('../internals/task').set;
-var Observer = global.MutationObserver || global.WebKitMutationObserver;
+var userAgent = require('../internals/user-agent');
+var MutationObserver = global.MutationObserver || global.WebKitMutationObserver;
 var process = global.process;
 var Promise = global.Promise;
 var queueMicrotask = global.queueMicrotask;
@@ -33,11 +34,11 @@ if (!queueMicrotask) {
     notify = function () {
       process.nextTick(flush);
     };
-  // browsers with MutationObserver, except iOS Safari - https://github.com/zloirock/core-js/issues/339
-  } else if (Observer && !(global.navigator && global.navigator.standalone)) {
+  // browsers with MutationObserver, except iOS - https://github.com/zloirock/core-js/issues/339
+  } else if (MutationObserver && !/(iPhone|iPod|iPad).*AppleWebKit/i.test(userAgent)) {
     var toggle = true;
     var node = document.createTextNode('');
-    new Observer(flush).observe(node, { characterData: true }); // eslint-disable-line no-new
+    new MutationObserver(flush).observe(node, { characterData: true }); // eslint-disable-line no-new
     notify = function () {
       node.data = toggle = !toggle;
     };