[javascript] Google Script to see if text contains a value

I used the Google Apps Script method indexOf() and its results were wrong. So I wrote the small function Myindexof(), instead of indexOf:

function Myindexof(s,text)
{
  var lengths = s.length;
  var lengtht = text.length;
  for (var i = 0;i < lengths - lengtht + 1;i++)
  {
    if (s.substring(i,lengtht + i) == text)
      return i;
  }
  return -1;
}

var s = 'Hello!';
var text = 'llo';
if (Myindexof(s,text) > -1)
   Logger.log('yes');
else
   Logger.log('no');