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

samples/third_party/dromaeo/common/JSON.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.
 
 // Pure Dart implementation of JSON protocol.
 
 /**
  * Utility class to parse JSON and serialize objects to JSON.
  */
 class JSON {
@@ skipping 326 matching lines @@
   }
 
   final JsonTokenizer _tokenizer;
 
   JsonParser._internal(String json) : _tokenizer = new JsonTokenizer(json) {}
 
   _parseToplevel() {
     JsonToken token = _tokenizer.next();
     final result = _parseValue(token);
     token = _tokenizer.next();
-    if (token !== null) {
+    if (token != null) {
       throw 'Junk at the end';
     }
     return result;
   }
 
   _parseValue(final JsonToken token) {
-    if (token === null) {
+    if (token == null) {
       throw 'Nothing to parse';
     }
     switch (token.kind) {
       case JsonToken.STRING:
         return token.str;
 
       case JsonToken.NUMBER:
         return token.number;
 
       case JsonToken.NULL:
@@ skipping 42 matching lines @@
     _parseSequence(JsonToken.RBRACKET, (JsonToken token) {
       final value = _parseValue(token);
       array.add(value);
     });
 
     return array;
   }
 
   void _parseSequence(int endTokenKind, void parseElement(JsonToken token)) {
     JsonToken token = _tokenizer.next();
-    if (token === null) {
+    if (token == null) {
       throw 'Unexpected end of stream';
     }
     if (token.kind == endTokenKind) {
       return;
     }
 
     parseElement(token);
 
     token = _tokenizer.next();
-    if (token === null) {
+    if (token == null) {
       throw 'Expected either comma or terminator';
     }
     while (token.kind != endTokenKind) {
       _assertTokenKind(token, JsonToken.COMMA);
 
       token = _tokenizer.next();
       parseElement(token);
 
       token = _tokenizer.next();
     }
   }
 
   void _assertTokenKind(JsonToken token, int kind) {
-    if (token === null || token.kind != kind) {
+    if (token == null || token.kind != kind) {
       throw 'Unexpected token kind: token = ${token}, expected kind = ${kind}';
     }
   }
 
   // TODO: consider factor out error throwing code and build more complicated
   // data structure to provide more info for a caller.
 }
 
 // TODO: proper base class.
 class JsonUnsupportedObjectType {
@@ skipping 47 matching lines @@
         needsEscape = true;
       }
       charCodes.add(charCode);
     }
     sb.add(needsEscape ? new String.fromCharCodes(charCodes) : s);
   }
 
   void _checkCycle(final object) {
     // TODO: use Iterables.
     for (int i = 0; i < _seen.length; i++) {
-      if (_seen[i] === object) {
+      if (identical(_seen[i], object)) {
         throw 'Cyclic structure';
       }
     }
     _seen.add(object);
   }
 
   void _stringify(final object) {
     if (object is num) {
       // TODO: use writeOn.
       _sb.add(_numberToString(object));
       return;
-    } else if (object === true) {
+    } else if (identical(object, true)) {
         _sb.add('true');
         return;
-    } else if (object === false) {
+    } else if (identical(object, false)) {
         _sb.add('false');
         return;
-    } else if (object === null) {
+    } else if (object == null) {
         _sb.add('null');
         return;
     } else if (object is String) {
         _sb.add('"');
         _escape(_sb, object);
         _sb.add('"');
         return;
     } else if (object is List) {
         _checkCycle(object);
         List a = object;
@@ skipping 22 matching lines @@
             _sb.add(',');
           }
         });
         _sb.add('}');
         return;
     } else {
         throw const JsonUnsupportedObjectType();
     }
   }
 }