var strStr = function( needle,haystack ) {

   // needle cannot be longer than haystack
   if(haystack.length < needle.length)
     return null;
   // needle is empty string
   if( needle.length === 0){
     return null;
   }
   // both strings are same
   if(haystack == needle){
     return true;
   }

   // lookahead to check needle in haystack
   for(var i=0; i < haystack.length;i++){
     var matching = false;
     if(haystack[i] === needle[0]){
       matching = true;
       var count = 1;
       while(matching){
         // all characters in the needle have been checked
         if(count==needle.length) {
           return true;
         }
         if(haystack[i+count] !== needle[count]){
           matching=false;
         }
         count++;
       }
     }
   }
   return null;
 };