diff --git a/sdk/lib/_internal/lib/async_patch.dart b/sdk/lib/_internal/lib/async_patch.dart
index dede2552bcd..cd5890d595f 100644
--- a/sdk/lib/_internal/lib/async_patch.dart
+++ b/sdk/lib/_internal/lib/async_patch.dart
@@ -14,8 +14,7 @@ import 'dart:_isolate_helper' show
     TimerImpl,
     leaveJsAsync,
     enterJsAsync,
-    isWorker,
-    globalThis;
+    isWorker;
 
 import 'dart:_foreign_helper' show JS;
 
@@ -46,7 +45,7 @@ class _AsyncRun {
       _initializeScheduleImmediate();
 
   static Function _initializeScheduleImmediate() {
-    if (JS('', '#.scheduleImmediate', globalThis) != null) {
+    if (JS('', 'self.scheduleImmediate') != null) {
       return _scheduleImmediateJsOverride;
     }
     // TODO(9002): don't use the Timer to enqueue the immediate callback.
@@ -60,8 +59,7 @@ class _AsyncRun {
       callback();
     };
     enterJsAsync();
-    JS('void', '#.scheduleImmediate(#)',
-       globalThis,
+    JS('void', 'self.scheduleImmediate(#)',
        convertDartClosureToJS(internalCallback, 0));
   }
 
diff --git a/sdk/lib/_internal/lib/isolate_helper.dart b/sdk/lib/_internal/lib/isolate_helper.dart
index d41ad0b53a3..08f4a764793 100644
--- a/sdk/lib/_internal/lib/isolate_helper.dart
+++ b/sdk/lib/_internal/lib/isolate_helper.dart
@@ -228,12 +228,12 @@ class _Manager {
         "(function (f, a) { return function (e) { f(a, e); }})(#, #)",
         DART_CLOSURE_TO_JS(IsolateNatives._processWorkerMessage),
         mainManager);
-    JS("void", r"#.onmessage = #", globalThis, function);
+    JS("void", r"self.onmessage = #", function);
     // We define dartPrint so that the implementation of the Dart
     // print method knows what to call.
     // TODO(ngeoffray): Should we forward to the main isolate? What if
     // it exited?
-    JS('void', r'#.dartPrint = function (object) {}', globalThis);
+    JS('void', r'self.dartPrint = function (object) {}');
   }
 
 
@@ -403,10 +403,8 @@ class _IsolateContext implements IsolateContext {
         // don't print it.
         return;
       }
-      if (JS('bool', '#.console != null && '
-                     'typeof #.console.error == "function"',
-                     globalThis, globalThis)) {
-        JS('void', '#.console.error(#, #)', globalThis, error, stackTrace);
+      if (JS('bool', '!!self.console && !!self.console.error')) {
+        JS('void', 'self.console.error(#, #)', error, stackTrace);
       } else {
         print(error);
         if (stackTrace != null) print(stackTrace);
@@ -685,11 +683,9 @@ class _MainManagerStub {
 const String _SPAWNED_SIGNAL = "spawned";
 const String _SPAWN_FAILED_SIGNAL = "spawn failed";
 
-var globalThis = Primitives.computeGlobalThis();
-var globalWindow = JS('', "#.window", globalThis);
-var globalWorker = JS('', "#.Worker", globalThis);
-bool globalPostMessageDefined =
-    JS('', "#.postMessage !== (void 0)", globalThis);
+get globalWindow => JS('', "self.window");
+get globalWorker => JS('', "self.Worker");
+bool get globalPostMessageDefined => JS('bool', "!!self.postMessage");
 
 typedef _MainFunction();
 typedef _MainFunctionArgs(args);
@@ -869,7 +865,7 @@ class IsolateNatives {
   }
 
   static void _consoleLog(msg) {
-    JS("void", r"#.console.log(#)", globalThis, msg);
+    JS("void", r"self.console.log(#)", msg);
   }
 
   static _getJSFunctionFromName(String functionName) {
@@ -1712,8 +1708,7 @@ class TimerImpl implements Timer {
 
       enterJsAsync();
 
-      _handle = JS('int', '#.setTimeout(#, #)',
-                   globalThis,
+      _handle = JS('int', 'self.setTimeout(#, #)',
                    convertDartClosureToJS(internalCallback, 0),
                    milliseconds);
     } else {
@@ -1726,8 +1721,7 @@ class TimerImpl implements Timer {
       : _once = false {
     if (hasTimer()) {
       enterJsAsync();
-      _handle = JS('int', '#.setInterval(#, #)',
-                   globalThis,
+      _handle = JS('int', 'self.setInterval(#, #)',
                    convertDartClosureToJS(() { callback(this); }, 0),
                    milliseconds);
     } else {
@@ -1743,9 +1737,9 @@ class TimerImpl implements Timer {
       if (_handle == null) return;
       leaveJsAsync();
       if (_once) {
-        JS('void', '#.clearTimeout(#)', globalThis, _handle);
+        JS('void', 'self.clearTimeout(#)', _handle);
       } else {
-        JS('void', '#.clearInterval(#)', globalThis, _handle);
+        JS('void', 'self.clearInterval(#)', _handle);
       }
       _handle = null;
     } else {
@@ -1756,7 +1750,7 @@ class TimerImpl implements Timer {
   bool get isActive => _handle != null;
 }
 
-bool hasTimer() => JS('', '#.setTimeout', globalThis) != null;
+bool hasTimer() => JS('', 'self.setTimeout') != null;
 
 
 /**
diff --git a/sdk/lib/_internal/lib/js_helper.dart b/sdk/lib/_internal/lib/js_helper.dart
index 4fab0b2d7fc..8f87ac4f8cb 100644
--- a/sdk/lib/_internal/lib/js_helper.dart
+++ b/sdk/lib/_internal/lib/js_helper.dart
@@ -552,8 +552,6 @@ class Primitives {
     return JS('int', '#', hash);
   }
 
-  static computeGlobalThis() => JS('', 'function() { return this; }()');
-
   static _throwFormatException(String string) {
     throw new FormatException(string);
   }
@@ -721,7 +719,7 @@ class Primitives {
 
   static String currentUri() {
     // In a browser return self.location.href.
-    if (JS('bool', 'typeof self != "undefined"')) {
+    if (JS('bool', '!!self.location')) {
       return JS('String', 'self.location.href');
     }
 
diff --git a/sdk/lib/_internal/lib/preambles/d8.js b/sdk/lib/_internal/lib/preambles/d8.js
index e9650837f14..99fed2b15d3 100644
--- a/sdk/lib/_internal/lib/preambles/d8.js
+++ b/sdk/lib/_internal/lib/preambles/d8.js
@@ -4,14 +4,10 @@
 
 // Javascript preamble, that lets the output of dart2js run on V8's d8 shell.
 
-var setTimeout;
-var clearTimeout;
-var setInterval;
-var clearInterval;
-var dartMainRunner;
-var scheduleImmediate;
+(function(self) {
+  // Using strict mode to avoid accidentally defining global variables.
+  "use strict"; // Should be first statement of this function.
 
-(function() {
   // Event loop.
 
   // Task queue as cyclic list queue.
@@ -247,14 +243,17 @@ var scheduleImmediate;
     }
   }
 
-  dartMainRunner = function(main, args) {
+  // Global properties. "self" refers to the global object, so adding a
+  // property to "self" defines a global variable.
+  self.dartMainRunner = function(main, args) {
     // Initialize.
     var action = function() { main(args); }
     eventLoop(action);
   };
-  setTimeout = addTimer;
-  clearTimeout = cancelTimer;
-  setInterval = addInterval;
-  clearInterval = cancelTimer;
-  scheduleImmediate = addTask;
-})();
+  self.setTimeout = addTimer;
+  self.clearTimeout = cancelTimer;
+  self.setInterval = addInterval;
+  self.clearInterval = cancelTimer;
+  self.scheduleImmediate = addTask;
+  self.self = self;
+})(this);
diff --git a/sdk/lib/_internal/lib/preambles/jsshell.js b/sdk/lib/_internal/lib/preambles/jsshell.js
index f24555fd544..e3b4f1aae35 100644
--- a/sdk/lib/_internal/lib/preambles/jsshell.js
+++ b/sdk/lib/_internal/lib/preambles/jsshell.js
@@ -3,3 +3,12 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // Javascript preamble, that lets the output of dart2js run on JSShell.
+
+(function(self) {
+  // Using strict mode to avoid accidentally defining global variables.
+  "use strict"; // Should be first statement of this function.
+
+  // Global properties. "self" refers to the global object, so adding a
+  // property to "self" defines a global variable.
+  self.self = self;
+})(this)
diff --git a/sdk/lib/js/dart2js/js_dart2js.dart b/sdk/lib/js/dart2js/js_dart2js.dart
index 84ec8f35670..27fac2e1e9d 100644
--- a/sdk/lib/js/dart2js/js_dart2js.dart
+++ b/sdk/lib/js/dart2js/js_dart2js.dart
@@ -97,7 +97,7 @@ import 'dart:_interceptors' show JavaScriptObject, UnknownJavaScriptObject;
 import 'dart:_js_helper' show Primitives, convertDartClosureToJS,
     getIsolateAffinityTag;
 
-final JsObject context = _wrapToDart(Primitives.computeGlobalThis());
+final JsObject context = _wrapToDart(JS('', 'self'));
 
 _convertDartFunction(Function f, {bool captureThis: false}) {
   return JS('',