How to test if a variable is empty - including an empty object or empty array

empty.js

function empty(data)
{
  if(typeof(data) == 'number' || typeof(data) == 'boolean')
  { 
    return false; 
  }
  if(typeof(data) == 'undefined' || data === null)
  {
    return true; 
  }
  if(typeof(data.length) != 'undefined')
  {
    return data.length == 0;
  }
  var count = 0;
  for(var i in data)
  {
    if(data.hasOwnProperty(i))
    {
      count ++;
    }
  }
  return count == 0;
}