Triage Expect.

dart/frog/leg/lib/js_helper.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('js_helper');
 
 #import('coreimpl.dart');
 
 #source('date_helper.dart');
 
 /**
   * Returns true if both arguments are numbers.
   * If only the first argument is a number, throws the given message as
   * exception.
   */
 bool checkNumbers(var a, var b, var message) {
   if (a is num) {
     if (b is num) {
       return true;
     } else {
       checkNull(b);
       throw new IllegalArgumentException(message);
     }
   }
   return false;
 }
 
 
 bool isJSArray(var value) {
-  return JS("bool", @"$0.constructor === Array", value);
+  return value !== null && JS("bool", @"$0.constructor === Array", value);

[ngeoffray, 2012/02/21 12:23:51]

No need.

 }
 
 
 add(var a, var b) {
   if (checkNumbers(a, b, "num+ expects a number as second operand.")) {
     return JS("num", @"$0 + $1", a, b);
   } else if (a is String) {
     b = b.toString();
     if (b is String) {
       return JS("String", @"$0 + $1", a, b);
@@ skipping 912 matching lines @@
 
 builtin$contains$2(receiver, other, startIndex) {
   checkNull(receiver);
   if (receiver is !String) {
     return UNINTERCEPTED(receiver.contains(other, startIndex));
   }
   checkNull(other);
   if (other is !String) {
     throw 'String.contains with non-String is not implemented';
   }
-  if ((startIndex !== null) || (startIndex is !num)) {
+  if ((startIndex !== null) && (startIndex is !num)) {
     throw new IllegalArgumentException(startIndex);
   }
   return receiver.indexOf(other, startIndex) >= 0;
 }
 
 builtin$endsWith$1(receiver, other) {
   checkNull(receiver);
   if (receiver is !String) return UNINTERCEPTED(receiver.endsWith(other));
 
   checkNull(other);
@@ skipping 160 matching lines @@
 builtin$hashCode$0(receiver) {
   if (receiver is num) return receiver & 0x1FFFFFFF;
   if (receiver is String) {
     throw 'String.hashCode is not implemented';
   }
   if (isJSArray(receiver)) {
     throw 'List.hashCode is not implemented';
   }
   return UNINTERCEPTED(receiver.hashCode());
 }