a === b -> identical(a, b)

sdk/lib/_internal/compiler/implementation/lib/interceptors.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('dart:_interceptors');
 
 #import('dart:collection');
 
 add$1(var receiver, var value) {
   if (isJsArray(receiver)) {
@@ skipping 48 matching lines @@
     if (newLength < 0) throw new RangeError.value(newLength);
     checkGrowable(receiver, 'set length');
     JS('void', r'#.length = #', receiver, newLength);
   } else {
     UNINTERCEPTED(receiver.length = newLength);
   }
   return newLength;
 }
 
 toString(var value) {
-  if (JS('bool', r'typeof # == "object" && # !== null', value, value)) {
+  if (JS('bool', r'typeof # == "object" && # != null', value, value)) {
     if (isJsArray(value)) {
       return Collections.collectionToString(value);
     } else {
       return UNINTERCEPTED(value.toString());
     }
   }
   if (JS('bool', r'# === 0 && (1 / #) < 0', value, value)) {
     return '-0.0';
   }
   if (value == null) return 'null';
@@ skipping 600 matching lines @@
   } else if (isJsArray(receiver)) {
     return getOrCreateCachedRuntimeType('List');
   } else {
     return UNINTERCEPTED(receiver.runtimeType);
   }
 }
 
 // TODO(lrn): These getters should be generated automatically for all
 // intercepted methods.
 get$toString(receiver) => () => toString(receiver);