I'm writing a simple jQuery plugin, but I'm having trouble being able to use multiple instances on a page.

For instance, here is a sample plugin to illustrate my point:

(function($) {
  $.fn.samplePlugin = function(options) {
    if (typeof foo != 'undefined')
    {
      alert('Already defined!');
    } else {
      var foo = 'bar';
    }
  };
})(jQuery);

And then if I do this:

$(document).ready(function(){
  $('#myDiv').samplePlugin({}); // does nothing
  $('#myDiv2').samplePlugion({}); // alerts "Already defined!"
});

This is obviously an over-simplified example to get across the point. So my question is, how do I have two separate instances of the plugin? I'd like to be able to use it across multiple instances on the same page.

I'm guessing that part of the problem might be with defining the variables in a global scope. How can I define them unique to that instance of the plugin then?

Thank you for your guidance!