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

compiler/javatests/com/google/dart/compiler/parser/StringBuffer.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.
 
 /**
  * The StringBuffer class is useful for concatenating strings
  * efficiently. Only on a call to [toString] are the strings
  * concatenated to a single String.
  */
 class StringBuffer implements OutputStream {
@@ skipping 31 matching lines @@
    * Returns the length of the buffer.
    */
   int get length {
     return length_;
   }
 
   /**
    * Appends [str] to the buffer.
    */
   void append(String str) {
-    if (str === null || str.isEmpty) return;
+    if (str == null || str.isEmpty) return;
     buffer_.add(str);
     length_ += str.length;
   }
 
   /**
    * Appends all items in [strings] to the buffer.
    */
   void appendAll(Collection<String> strings) {
     strings.forEach((str) { append(str); });
   }
@@ skipping 17 matching lines @@
     buffer_.add(result);
     // Since we track the length at each append operation, there is no
     // need to update it in this function.
     return result;
   }
 
   GrowableArray<String> buffer_;
   int length_;
   final bool closed = false;
 }