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

tests/compiler/dart2js/mock_compiler.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 mock_compiler;
 
 import 'dart:uri';
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart' as api;
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
@@ skipping 117 matching lines @@
   void reportError(Node node, var message) {
     if (message is String && message.startsWith("no library name found in")) {
       // TODO(ahe): Fix the MockCompiler to not have this problem.
       return;
     }
     errors.add(new WarningMessage(node, message.message));
   }
 
   void reportMessage(SourceSpan span, var message, api.Diagnostic kind) {
     var diagnostic = new WarningMessage(null, message.message);
-    if (kind === api.Diagnostic.ERROR) {
+    if (identical(kind, api.Diagnostic.ERROR)) {

[Lasse Reichstein Nielsen, 2012/11/12 13:10:41]

Consider whether == would do, since Diagnostic probably don't override
operator==.

[floitsch, 2012/11/12 22:18:43]

Done.

       errors.add(diagnostic);
     } else {
       warnings.add(diagnostic);
     }
   }
 
   void reportDiagnostic(SourceSpan span, String message, var kind) {
     print(message);
   }
 
@@ skipping 27 matching lines @@
     Element mockElement =
         new Element(buildSourceString(''), ElementKind.FUNCTION, mainApp);
     ResolverVisitor visitor =
         new ResolverVisitor(this, mockElement,
                             new CollectingTreeElements(mockElement));
     visitor.scope = new MethodScope(visitor.scope, mockElement);
     return visitor;
   }
 
   parseScript(String text, [LibraryElement library]) {
-    if (library === null) library = mainApp;
+    if (library == null) library = mainApp;
     parseUnit(text, this, library);
   }
 
   void scanBuiltinLibraries() {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
   LibraryElement scanBuiltinLibrary(String name) {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
   void importCoreLibrary(LibraryElement library) {
     scanner.importLibrary(library, coreLibrary, null);
   }
 
   // The mock library doesn't need any patches.
   Uri resolvePatchUri(String dartLibraryName) => null;
 
   Script readScript(Uri uri, [ScriptTag node]) {
     SourceFile sourceFile = sourceFiles[uri.toString()];
-    if (sourceFile === null) throw new ArgumentError(uri);
+    if (sourceFile == null) throw new ArgumentError(uri);
     return new Script(uri, sourceFile);
   }
 }
 
 void compareWarningKinds(String text, expectedWarnings, foundWarnings) {
   var fail = (message) => Expect.fail('$text: $message');
   Iterator<MessageKind> expected = expectedWarnings.iterator();
   Iterator<WarningMessage> found = foundWarnings.iterator();
   while (expected.hasNext && found.hasNext) {
     Expect.equals(expected.next(), found.next().message.kind);
@@ skipping 36 matching lines @@
   operator []=(Node node, Element element) {
     map[node] = element;
   }
 
   operator [](Node node) => map[node];
 
   void remove(Node node) {
     map.remove(node);
   }
 }