Copy JSSyntaxRegExp from frog.

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');
+#source('regexp_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;
@@ skipping 772 matching lines @@
   if (value is !int) throw new IllegalArgumentException(value);
   return value;
 }
 
 checkBool(value) {
   checkNull(value);
   if (value is !bool) throw new IllegalArgumentException(value);
   return value;
 }
 
+checkString(value) {
+  checkNull(value);

[kasperl, 2012/02/21 07:35:17]

Would it be simpler to rewrite some of these to do a positive is test instead?
Something like:

   if (value is String) return value;
   throw new IllegalArgumentException(value);

That way you don't need the explicit null check.

+  if (value is !String) throw new IllegalArgumentException(value);
+  return value;
+}
+
 builtin$isNegative$0(receiver) {
   checkNull(receiver);
   if (receiver is num) {
     return (receiver === 0) ? (1 / receiver) < 0 : receiver < 0;
   } else {
     return UNINTERCEPTED(receiver.isNegative());
   }
 }
 
 builtin$isNaN$0(receiver) {
@@ skipping 323 matching lines @@
 builtin$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());
 }