javascript to search a string for text, in reverse

javascript to search a string for text, in reverse:

 //similar to string.indexOf(), except that it starts searching at the end of the string.  
 jsUtils.reverseIndexOf = function (toSearch, toFind) {  
   if (toFind.length != 1) {  
     throw 'jsUtils.reverseIndexOf() - only implementeed for searching for 1 character';  
   }  
   var lastIndex = 0;  
   for (var i = 0; i < toSearch.length; i++) {  
     if (toSearch[toSearch.length - i - 1] === toFind) {  
       lastIndex = toSearch.length - i;  
       break;  
     }  
   }  
   return lastIndex - 1;  
 };  

example usage:

 jsUtils.reverseIndexOf('abcd', 'a')  
 0  
 jsUtils.reverseIndexOf('abcda', 'b')  
 1  
 jsUtils.reverseIndexOf('abcda', 'x')  
 -1  
 jsUtils.reverseIndexOf('abcda', 'a')  
 4  
 jsUtils.reverseIndexOf('abcda', '4')  
 -1  
 jsUtils.reverseIndexOf('abcda', '')  
 "jsUtils.reverseIndexOf() - only implementeed for searching for 1 character"  
 jsUtils.reverseIndexOf('abcda', 'ff')  
 "jsUtils.reverseIndexOf() - only implementeed for searching for 1 character"