Fix for issue 351 - lastIndexOf.

src/string.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 102 matching lines @@
   if (index < 0) index = 0;
   if (index > subject_str_len) index = subject_str_len;
   if (pattern_str_len + index > subject_str_len) return -1;
   return %StringIndexOf(subject_str, pattern_str, index);
 }
 
 
 // ECMA-262 section 15.5.4.8
 function StringLastIndexOf(searchString /* position */) {  // length == 1
   var sub = ToString(this);
+  var subLength = sub.length;
   var pat = ToString(searchString);
-  var index = (%_ArgumentsLength() > 1)
-      ? ToNumber(%_Arguments(1) /* position */)
-      : $NaN;
-  var firstIndex;
-  if ($isNaN(index)) {
-    firstIndex = sub.length - pat.length;
-  } else {
-    firstIndex = TO_INTEGER(index);
-    if (firstIndex + pat.length > sub.length) {
-      firstIndex = sub.length - pat.length;
+  var patLength = pat.length;
+  var index = subLength - patLength;
+  if (%_ArgumentsLength() > 1) {
+    var position = ToNumber(%_Arguments(1));
+    if (!$isNaN(position)) {
+      position = TO_INTEGER(position);
+      if (position < 0) {
+        position = 0;
+      }
+      if (position + patLength < subLength) {
+        index = position
+      }
     }
   }
-  return %StringLastIndexOf(sub, pat, firstIndex);
+  if (index < 0) {
+    return -1;
+  }
+  return %StringLastIndexOf(sub, pat, index);
 }
 
 
 // ECMA-262 section 15.5.4.9
 //
 // This function is implementation specific.  For now, we do not
 // do anything locale specific.
 function StringLocaleCompare(other) {
   if (%_ArgumentsLength() === 0) return 0;
 
@@ skipping 716 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();