function recursiveSearch(aLow, aHigh, aNeedle, aHaystack, aCompare) {
    // This function terminates when one of the following is true:
    //
    //   1. We find the exact element we are looking for.
    //
    //   2. We did not find the exact element, but we can return the next
    //      closest element that is less than that element.
    //
    //   3. We did not find the exact element, and there is no next-closest
    //      element which is less than the one we are searching for, so we
    //      return null.
    var mid = Math.floor((aHigh - aLow) / 2) + aLow;
    var cmp = aCompare(aNeedle, aHaystack[mid], true);
    if (cmp === 0) {
      // Found the element we are looking for.
      return aHaystack[mid];
    }
    else if (cmp > 0) {
      // aHaystack[mid] is greater than our needle.
      if (aHigh - mid > 1) {
        // The element is in the upper half.
        return recursiveSearch(mid, aHigh, aNeedle, aHaystack, aCompare);
      }
      // We did not find an exact match, return the next closest one
      // (termination case 2).
      return aHaystack[mid];
    }
    else {
      // aHaystack[mid] is less than our needle.
      if (mid - aLow > 1) {
        // The element is in the lower half.
        return recursiveSearch(aLow, mid, aNeedle, aHaystack, aCompare);
      }
      // The exact needle element was not found in this haystack. Determine if
      // we are in termination case (2) or (3) and return the appropriate thing.
      return aLow < 0
        ? null
        : aHaystack[aLow];
    }
  }
Recursive implementation of binary search.

@param aLow Indices here and lower do not contain the needle.
@param aHigh Indices here and higher do not contain the needle.
@param aNeedle The element being searched for.
@param aHaystack The non-empty array being searched.
@param aCompare Function which takes two elements and returns -1, 0, or 1.