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

tests/corelib/expando_test.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.
 
 class ExpandoTest {
   static Expando<int> visits;
 
   static testMain() {
     visits = new Expando<int>('visits');
     var legal = [ new Object(),
                   new List(), [1,2,3], const [1,2,3],
                   new Map(), {'x':1,'y':2}, const {'x':1,'y':2},
                   new Expando(), new Expando('horse') ];
     for (var object in legal) {
       testNamedExpando(object);
       testUnnamedExpando(object);
     }
     for (var object in legal) {
       Expect.equals(2, visits[object]);
     }
     testIllegal();
   }
 
   static visit(object) {
     int count = visits[object];
-    count = (count === null) ? 1 : count + 1;
+    count = (count == null) ? 1 : count + 1;
     visits[object] = count;
   }
 
   static testNamedExpando(object) {
     Expando<int> expando = new Expando<int>('myexpando');
     Expect.equals('myexpando', expando.name);
     Expect.isTrue(expando.toString().startsWith('Expando:myexpando'));
     testExpando(expando, object);
   }
 
@@ skipping 35 matching lines @@
     Expect.throws(() => expando[42.87], (exception)
                   => exception is ArgumentError);
     Expect.throws(() => expando[true], (exception)
                   => exception is ArgumentError);
     Expect.throws(() => expando[false], (exception)
                   => exception is ArgumentError);
   }
 }
 
 main() => ExpandoTest.testMain();