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

runtime/lib/array.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.
 
 
 // TODO(srdjan): Use shared array implementation.
 class _ObjectArray<E> implements List<E> {
 
   factory _ObjectArray(int length) native "ObjectArray_allocate";
 
@@ skipping 71 matching lines @@
 
   bool every(bool f(E element)) {
     return Collections.every(this, f);
   }
 
   bool some(bool f(E element)) {
     return Collections.some(this, f);
   }
 
   bool get isEmpty {
-    return this.length === 0;
+    return this.length == 0;
   }
 
   void sort([Comparator<E> compare = Comparable.compare]) {
     coreSort(this, compare);
   }
 
   int indexOf(E element, [int start = 0]) {
     return Arrays.indexOf(this, element, start, this.length);
   }
 
   int lastIndexOf(E element, [int start = null]) {
-    if (start === null) start = length - 1;
+    if (start == null) start = length - 1;
     return Arrays.lastIndexOf(this, element, start);
   }
 
   Iterator<E> iterator() {
     return new _FixedSizeArrayIterator<E>(this);
   }
 
   void add(E element) {
     throw new UnsupportedError(
         "Cannot add to a non-extendable array");
@@ skipping 109 matching lines @@
 
   bool every(bool f(E element)) {
     return Collections.every(this, f);
   }
 
   bool some(bool f(E element)) {
     return Collections.some(this, f);
   }
 
   bool get isEmpty {
-    return this.length === 0;
+    return this.length == 0;
   }
 
   void sort([Comparator<E> compare]) {
     throw new UnsupportedError(
         "Cannot modify an immutable array");
   }
 
   String toString() {
     return Collections.collectionToString(this);
   }
 
   int indexOf(E element, [int start = 0]) {
     return Arrays.indexOf(this, element, start, this.length);
   }
 
   int lastIndexOf(E element, [int start = null]) {
-    if (start === null) start = length - 1;
+    if (start == null) start = length - 1;
     return Arrays.lastIndexOf(this, element, start);
   }
 
   Iterator<E> iterator() {
     return new _FixedSizeArrayIterator<E>(this);
   }
 
   void add(E element) {
     throw new UnsupportedError(
         "Cannot add to an immutable array");
@@ skipping 44 matching lines @@
     if (!hasNext) {
       throw new StateError("No more elements");
     }
     return _array[_pos++];
   }
 
   final List<E> _array;
   final int _length;  // Cache array length for faster access.
   int _pos;
 }