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

tests/compiler/dart2js/type_checker_test.dart

 // Copyright (c) 2011, 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.
 
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
        hide SourceString;
 import '../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/tree/tree.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/util/util.dart';
 import 'mock_compiler.dart';
@@ skipping 398 matching lines @@
 }
 
 DartType analyzeType(String text) {
   var node = parseExpression(text);
   TypeCheckerVisitor visitor =
       new TypeCheckerVisitor(compiler, new TreeElementMapping(null), types);
   return visitor.analyze(node);
 }
 
 analyzeTopLevel(String text, [expectedWarnings]) {
-  if (expectedWarnings === null) expectedWarnings = [];
+  if (expectedWarnings == null) expectedWarnings = [];
   if (expectedWarnings is !List) expectedWarnings = [expectedWarnings];
 
   LibraryElement library = mockLibrary(compiler, text);
 
   Link<Element> topLevelElements = parseUnit(text, compiler, library);
 
   for (Link<Element> elements = topLevelElements;
        !elements.isEmpty;
        elements = elements.tail) {
     Node node = elements.head.parseNode(compiler);
     TreeElements mapping = compiler.resolver.resolve(elements.head);
     TypeCheckerVisitor checker =
         new TypeCheckerVisitor(compiler, mapping, types);
     compiler.clearWarnings();
     checker.analyze(node);
     compareWarningKinds(text, expectedWarnings, compiler.warnings);
   }
 }
 
 analyze(String text, [expectedWarnings]) {
-  if (expectedWarnings === null) expectedWarnings = [];
+  if (expectedWarnings == null) expectedWarnings = [];
   if (expectedWarnings is !List) expectedWarnings = [expectedWarnings];
 
   Token tokens = scan(text);
   NodeListener listener = new NodeListener(compiler, null);
   Parser parser = new Parser(listener);
   parser.parseStatement(tokens);
   Node node = listener.popNode();
   Element function = new Element(
       buildSourceString(''), ElementKind.FUNCTION, compiler.mainApp);
   TreeElements elements = compiler.resolveNodeStatement(node, function);
   TypeCheckerVisitor checker = new TypeCheckerVisitor(compiler, elements,
                                                                 types);
   compiler.clearWarnings();
   checker.analyze(node);
   compareWarningKinds(text, expectedWarnings, compiler.warnings);
 }
 
 analyzeIn(ClassElement classElement, String text, [expectedWarnings]) {
-  if (expectedWarnings === null) expectedWarnings = [];
+  if (expectedWarnings == null) expectedWarnings = [];
   if (expectedWarnings is !List) expectedWarnings = [expectedWarnings];
 
   Token tokens = scan(text);
   NodeListener listener = new NodeListener(compiler, null);
   Parser parser = new Parser(listener);
   parser.parseStatement(tokens);
   Node node = listener.popNode();
   classElement.ensureResolved(compiler);
   TreeElements elements = compiler.resolveNodeStatement(node, classElement);
   TypeCheckerVisitor checker = new TypeCheckerVisitor(compiler, elements,
                                                                 types);
   compiler.clearWarnings();
   checker.currentClass = classElement;
   checker.analyze(node);
   compareWarningKinds(text, expectedWarnings, compiler.warnings);
 }